I Disagree, the tribulation will be 3.5 years, and it will start when the future evil human man is revealed to the world
It is not "the" tribulation - in the bible. Jesus called that time "great tribulation".
When does it start ?
Jesus said in Matthew 24:15...
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: )
So we go to Daniel 12:11-12
11 And from the time that the daily sacrifice shall be taken away, and the abomination that maketh desolate set up, there shall be a thousand two hundred and ninety days.
12 Blessed is he that waiteth, and cometh to the thousand three hundred and five and thirty days.
So it is a thing "set up".
Being a thing "set up" , the abomination of desolation is not the revealing of the man of sin.
The revealing of the man of sin will actually take place a little before the abomination of desolation is setup.
The revealing of the man of sin will be when the Antichrist goes into the temple, sits, claiming to be God, in 2Thessalonians2:4. That act will be the "transgression of desolation" found in Daniel 8:12-13.
the transgression of desolation - the act by the Antichrist, revealing him as the man of sin.
followed by....
the abomination of desolation - the statue image of the beast, placed on the temple mount.
the little horn>prince who shall come>the Antichrist>the revealed man of sin>the beast - are all the same person at different stages on his path to the lake of fire.
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There is no "3 1/2 years", stated as such in the bible.
There are three ways that people mistakenly base that term. The three ways sound rationale, but in bible prophecy, their rationale leads them amiss in their interpretations (I say that respectfully of my brothers and sisters in Christ, and not being condescending).
The three ways....
1. They think that the expression a time/times/half time is a biblical way of saying 3 1/2 years. But it is not. The time/times/half time is actually a little less or a little more than 3 1/2 years depending upon the context.
a time/times/half time is "nominally 3 1/2 years" to give us an approximation, but it is not exactly 3 1/2 years. Just like a two by four, 2x4 in lumber that you buy down at Home Depot, Lowe's, etc. is not actually 2 inches x 4 inches. It is "nominally" 2x4 - but less, if you were to actually measure it - 1 3/4 inches x 3 1/2 inches.
2. The other way is by people doing
unit conversions - 1260 days to 3 1/2 years, and 42 months to 3 1/2 years. But that is a mistake to do so because the time expressions 1260 days and 42 months are there expressed differently for a reason - and are not "exact" equivalents to each other i
n bible prophecy. If a person were baking a cake, or solving an engineering problem - then , yes, those sorts of conversions of units would apply - but not in bible prophecy.
3. They read Daniel 9:27, which says "in the midst of the week" - and take the midst of the week as being the exact middle of the 7 years. And conclude 3 1/2 years.
When what the verse is actually meaning is in the middle part of the week. Not the exact middle day.