Only the ONE persons opinion matters, and HIS name is the God Almighty YaHWeH; (not ' what do you think'- what do " I " think or million others scientists, theologians or rest of " them". The whole concept of tribulation (Seven years ?) has its origin in Daniel's vision of the seventy weeks (Dan.9:24-27)…
Where shall I start ? giving answer to "when, what, where…" ?- since the time of tribulation is during Daniel's Seventh Week, the nation of Israel will be affected by the tribulation before the seventh week begins.. how long before ? - when Antichrist rises at the beginning of the Week; will make a seven years covenant with Israel protecting them as a nation. When Jews won't accept one religion dominance…--
(Just these days the Roman-Catholic-Pope has invited both the
Israel's prime min. as well as Palestinian leader to Rome for joint prayer (! ) and they accepted.)
-- concerning the time of tribulation's duration , will be the whole of Daniel's seventh Week, (Dan.9:27). After three and one half years Antichrist will brake his covenant with Israel, - then the great tribulation more severe fulfillment will continue of Revelation 10:1- 19:21) . During this time God's wrath will be poured out upon mankind for their wickedness and corruption which is exceeding the´days of Noah and Lot. The truth of God would be rejected by all men who will now believe lies and deception of the Antichrist.
Reading carefully the Bible we can see that the reign of Antichrist won't be over the whole world / only over the kingdom that is to be formed inside the old Roman Empire. Revel. .8: 7-12 indicates the judgment being upon the men having mark of the beast; the sixth trumpet kills only a third part of men (Revel.9:12-21).