Scriptures showing the Tribulation will last 7 years:

These verses speak of the Abomination of Desolation & the 7 year Tribulation (my words in italics):

Paul doesn't use the words "abomination of desolation", but he describes The "False Christ" as the deception & blasphemy in the Temple;

[2Thess 2:3] Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
[2Thess 2:4] Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
[2Thess 2:9] Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
[2Thess 2:10] And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
[2Thess 2:11] And for this cause God shall send them strong delusion, that they should believe a lie:

Jesus links "a False Christ, & False Christs" , and also this deception, to the abomination of desolation in Daniel

[Mark 13:14] But when ye shall see the abomination of desolation, spoken of by Daniel the prophet, standing where it ought not, (let him that readeth understand,) then let them that be in Judaea flee to the mountains:
[Mark 13:21] And then if any man shall say to you, Lo, here is Christ; or, lo, he is there; believe him not:
[Mark 13:22] For false Christs and false prophets shall rise, and shall shew signs and wonders, to seduce, if it were possible, even the elect.

In parallel gospel of Matthew, Jesus specifically mentions the False Christ in the "holy place/Secret chambers", or Temple;

[Mat 24:15] When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand:)
[Mat 24:24] For there shall arise false Christs, and false prophets, and shall shew great signs and wonders;
insomuch that, if it were possible, they shall deceive the very elect.
[Mat 24:25] Behold, I have told you before.
[Mat 24:26] Wherefore if they shall say unto you, Behold, he is in the desert; go not forth: behold, he is in the secret chambers; believe it not.

In Daniel, the timing of the abomination of desolation is given; in the middle of the week, or 7 years, and a 1290 days time period, which is 30 days longer than 3.5 years.

[Dan 9:27] And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate.

[Dan 11:31] And arms shall stand on his part, and they shall pollute the sanctuary of strength, and shall take away the daily sacrifice, and they shall place the abomination that maketh desolate.

[Dan 12:11] And from the time that the daily sacrifice shall be taken away, and [until?] the abomination that maketh desolate set up, there shall be a thousand two hundred and ninety days.

Revelation links the 3.5 years, the blasphemy of the abomination, war on the saints, and many other things with Daniel's vision.

[Rev 13:4] And they worshipped the dragon which gave power unto the beast: and they worshipped the beast, saying, Who is like unto the beast? who is able to make war with him?
[Rev 13:5] And there was given unto him a mouth speaking great things and blasphemies; and power was
given unto him to continue forty and two months.
[Rev 13:6] And he opened his mouth in blasphemy against God, to blaspheme his name, and his tabernacle,
and them that dwell in heaven.
[Rev 13:7] And it was given unto him to make war with the saints, and to overcome them: and power was
given him over all kindreds, and tongues, and nations.

This is the same "AntiChrist/Beast/Horn" as Daniel's vision, speaking the same crime of blasphemy, ("I am God" Of 2 Thess) and the time length of "Great Tribulation" is the same, 3.5 years; 42 months in Rev, and 3 1/2 times in Daniel:

[Dan 7:21] I beheld, and the same horn made war with the saints, and prevailed against them;

[Dan 7:25] And he shall speak great words against the most High, and shall wear out the saints of the most
High, and think to change times and laws: and they shall be given into his hand until a time and times and the dividing of time.

This 3.5 years is the second half of the 7 years.  The blasphemy and the war on the saints concludes with Satan's destruction, but is preceeded by the time of the two witnesses.

[Rev 11:1] And there was given me a reed like unto a rod: and the angel stood, saying, Rise, and measure the temple of God, and the altar, and them that worship therein.
[Rev 11:2] But the court which is without the temple leave out, and measure it not; for it is given unto the
Gentiles: and the holy city shall they tread under foot forty and two months.
[Rev 11:3] And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth.
[Rev 11:4] These are the two olive trees, and the two candlesticks standing before the God of the earth.
[Rev 11:5] And if any man will hurt them, fire proceedeth out of their mouth, and devoureth their enemies: and if any man will hurt them, he must in this manner be killed.
[Rev 11:6] These have power to shut heaven, that it rain not in the days of their prophecy: and have power over waters to turn them to blood, and to smite the earth with all plagues, as often as they will.
[Rev 11:7] And when they shall have finished their testimony, the beast that ascendeth out of the bottomless pit shall make war against them, and shall overcome them, and kill them.

So the 3.5 years of their witnessing preceedes the time when God allows Satan to ascend into the world and make war on the saints for  3.5 years.

And again, there is another verse, that speaks of tribulation, but it's not nearly so bad as when Satan is allowed to make war on the saints... because the saints are protected.

[Rev 12:6] And the woman fled into the wilderness, where she hath a place prepared of God, that they
should feed her there a thousand two hundred and threescore days.

Thus, these are two different 3.5 year periods, fitting into Daniel's 70th week, the final 7 years, which is split in the middle by the act of the abomination of desolation.

And all of this is preceeded by the comforting doctrine of the rapture; so that we need not fear nor look forward to this this time of Satan's arrival; but rather, so that we can keep our focus on Christ's return.

[1Thess 4:13] But I would not have you to be ignorant, brethren, concerning them which are asleep, that ye sorrow not, even as others which have no hope.
[1Thess 4:14] For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him.
[1Thess 4:15] For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep.
[1Thess 4:16] For the Lord himself shall descend from heaven with a shout, with the voice of the archangel,
and with the trump of God: and the dead in Christ shall rise first:
[1Thess 4:17] Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
[1Thess 4:18] Wherefore comfort one another with these words.

[2Thess 2:1] Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering
together unto him,
[2Thess 2:2] That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand.
[2Thess 2:16] Now our Lord Jesus Christ himself, and God, even our Father, which hath loved us, and hath
given us everlasting consolation and good hope through grace,
[2Thess 2:17] Comfort your hearts, and stablish you in every good word and work.

"For God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ," (1
Thessalonians 5:9)

"Because thou hast kept the word of my patience, I also will keep thee from the hour of
temptation, which shall come upon all the world, to try them that dwell upon the earth."
(Revelation 3:10)

But I will issue a warning, the pre tribulation rapture is not a guaranteed escape to Heaven for the lukewarm or those that tolerate evil...  Read Matthew 25; 1/2 the virgins go.  Read Rev 2-3, only 1/7 of the Churches seems righteous and faithful enough to be spared.

"Watch ye therefore, and pray always, that ye may be accounted worthy to escape all these things
that shall come to pass, and to stand before the Son of man." (Luke 21:36)

Read Ezekiel 38, 39.  Also known as the gog/magog war.  This should happen right after the rapture, and the "seven years" is the length of the tribulation.  Do not confuse this war with Armageddon (which happens at the end of the 7 years), even though many nations are coming against Isreal.  The AntiChrist forces should be claiming that this is Armageddon in order to deceive the world into accepting the one world government that will enslave and deceive the whole earth.

[Ezek 39:9] And they that dwell in the cities of Israel shall go forth, and shall set on fire andburn the weapons, both the shields and the bucklers, the bows and the arrows, and the handstaves, and the spears, and they shall burn them with fire seven years:

[Jer 30:7] Alas! for that day is great, so that none is like it: it is even the time of Jacob's trouble, but he shall be saved out of it.

Jacob's trouble is known as the tribulation.  Jacob had two times of "trouble" and each was a 7 year period.

First, there was the extra seven years he labored for Rachel.
Second, there was the seven year famine that drove him and his family down to Egypt.

An in depth look at each of these stories, with the knowledge of the Feast of Trumpets, and the Jewish Wedding shows that the rapture will happen before the seven year tribulation.

The first story takes us right to the knowledge of the bridal week. Jacob was deceived by Laban into marrying Leah instead of Rachel, when the mariage feast was held at the start of the bridal week.

Genesis 29:22-28 So Laban brought together all the people of the place and gave a feast. ...Finish this daughter's bridal week

If Laban had held the feast at the end of the bridal week, as the feast is at the end of the tribulation in Rev. 19, Jacob would not have been deceived.  Regardless, the time of marital intimacy, the rapture, happens at the beginning of the bridal week, which is a shadow of the tribulation week.  Further, the marriage of Leah started off the beginning of the 7 extra years of labor for Rachel.

The bridal week is also mentioned in Judges 14:1-18 ...And Samson made a feast there, as was customary for bridegrooms. ...If you can give me the answer within the seven days of the feast... She cried the whole seven days of the feast.

The second story of Jacob's trouble is the 7 year famine.  His son Joseph had been sold into Egypt by his brothers.  Joseph had a dream that prophesied the famine after 7 years of plenty.

Rapture symbols associated with Feast of Trumpets & Joseph in Egypt in Genesis

Joseph made the Feast of Trumpets a mandatory statute, ordinance, decree, a celebration in Egypt.  A full study of the Feast of Trumpets shows it symbolizes the rapture and the wedding of the Messiah.

[Pss 81:3] Blow the trumpet at the new moon, at the full moon, on our feast day.
[Pss 81:4] For it is a statute for Israel, an ordinance of the God of Jacob.
[Pss 81:5] He made it a decree in Joseph, when he went out over the land of Egypt. I hear a voice I had not known:
[Pss 81:6] "I relieved your shoulder of the burden; your hands were freed from the basket.
[Pss 81:7] In distress you called, and I delivered you; I answered you in the secret place of thunder; I tested you at the waters of
Meribah. [Selah]

[Exod 17:7.11] And he called the name of the place Massah and Meribah, because of the faultfinding of the children of Israel, and because they put the LORD to the proof by saying, "Is the LORD among us or not?"  (This is when Moses struck the rock and water came out, but it went wrong because Moses said he would provide the water, and not from the Lord.)

[Gen 41:45] And Pharaoh called Joseph's name Zaphenath-paneah; and he gave him in marriage Asenath, the daughter of Potiphera priest
of On. So Joseph went out over the land of Egypt.
[Gen 41:46] Joseph was thirty years old when he entered the service of Pharaoh king of Egypt. And Joseph went out from the presence of
Pharaoh, and went through all the land of Egypt.
[Gen 41:47] During the seven plenteous years the earth brought forth abundantly,

Joseph "went out over the land".  The same Hebrew words used in both accounts; these words can also mean "depart the earth".  As in "rapture".  And note, all this is BEFORE the 7 years of plenty, which is before the 7 years of famine, like the tribulation.

It seems almost a complete non-sequetor in Gen. 41:45, first the marriage, and then the going out over the land to prepare... I mean, how one
related to the other, and it's all in one verse!  Unless, --the two events are related, as in the rapture, where we are wed with Christ, going out
of the earth into the air over the land!!

The phrase, "I hear a voice" in Psalm 81:5 is like in Rev. 4:1, which also links the trumpet, and the open door, which is also a symbol of the Feast of Trumpets.

[Revelation 4:1] After this I looked, and, behold, a door was opened in heaven: and the first voice which I heard was as it were of a
trumpet talking with me; which said, Come up hither, and I will shew thee things which must be hereafter.

[Ezek 46:1] "Thus says the Lord GOD: The gate of the inner court that faces east shall be shut on the six working days; but on the sabbath day it shall be opened and on the day of the new moon it shall be opened.

Getting back to Daniel.

Chapter 3; the worship of the golden image and the furnace of fire.  One cannot help but to note the similarities between this story and Rev. 13, the mark of the beast that one must take in order to buy and sell, or ultimately face death by beheading.  So, we should already have in mind the similarities between Daniel and Revelation.

Daniel 4: The King becomes a beast for seven years, in order to make him know that God is the King of the world who establishes Kings by God's will.
[Dan 4:16] Let his heart be changed from man's, and let a beast's heart be given unto him; and let seven times pass over him.

[Dan 4:17] This matter is by the decree of the watchers, and the demand by the word of the holy ones: to the intent that the living may know that the most High ruleth in the kingdom of men, and giveth it to whomsoever he will, and setteth up over it the basest of men.

[Dan 4:33] The same hour was the thing fulfilled upon Nebuchadnezzar: and he was driven from men, and did eat grass as oxen, and his body was wet with the dew of heaven, till his hairs were grown like eagles' feathers, and his nails like birds' claws.

The King is made to be as a wild beast, which is how the world governments are described in Revelation, a wild beast.  Revelation uses "beast" 59 times.

[1Cor 10:11] Now all these things happened unto them for ensamples: and they are written for our admonition, upon
whom the ends of the world are come.

[1Cor 15:46] Howbeit that was not first which is spiritual, but that which is natural; and afterward that which is spiritual.

[Rev 13:4] And they worshipped the dragon which gave power unto the beast: and they worshipped the beast, saying, Who is like unto the beast? who is able to make war with him?
[Rev 13:5] And there was given unto him a mouth speaking great things and blasphemies; and power was given unto him to continue forty and two months.

(42 months is 3.5 years--the second half of the 7 year tribulation)

The King becomes a wild beast for seven times, which we know are seven years.  Even the wording of "times" instead of years should make us take special note that Revelation is trying to get us to look at the seven times that passed over the King, in Daniel 4.

[Dan 12:7.] And I heard the man clothed in linen, which was upon the waters of the river, when he held up his right hand and his left hand unto heaven, and sware by him that liveth for ever that it shall be for a time, times, and an half; and when he shall have accomplished to scatter the power of the holy people, all these things shall be finished.

Dan 12:7, linked with Rev. 13:5.  42 months, says that the 3.5 times is 3.5 years.

[Rev 12:14] And to the woman were given two wings of a great eagle, that she might fly into the wilderness, into her place, where she is nourished for a time, and times, and half a time, from the face of the serpent.

[Rev 12:6] And the woman fled into the wilderness, where she hath a place prepared of God, that they should feed her there a thousand two hundred and threescore days.

Again, the 3.5 times, are linked to 3.5 years, this time through the 1260 days.

(The other 42 months verse; 3.5 years:)
[Rev 11:2] But the court which is without the temple leave out, and measure it not; for it is given unto the Gentiles: and the holy city shall they tread under foot forty and two months.

(The other 1260 days verse; 3.5 years)
[Rev 11:3] And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth.

The purpose of the King's days as a beast, and the 7 year tribulation is similar.
So that all the world (not just the king) will know that God is the King of Kings, the Lord of Lords, the supreme ruler of the earth.

[Pss 12:6] The words of the LORD are pure words: as silver tried in a furnace of earth, purified seven times.

The Gospel & Salvation Message (my 'statement of faith' from the King James Bible)

 [Rom 5:8] But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us.
 [1John 1:8] If we say that we have no sin, we deceive ourselves, and the truth is not in us.
 [1John 1:9] If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
 [Rom 10:9] That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead,
 thou shalt be saved.
 [Rom 10:10] For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
 [Mat 10:32] Whosoever therefore shall confess me before men, him will I confess also before my Father which is in heaven.