Our 'fig tree' generation started when the fig tree (Israel) came to life; May 14, 1948 (Matt 24:32-34).
Add to this date 80 years (the maximum lifespan of a generation - Psalm 90:10); May 14, 1948 + 80 years = May 14, 2028
Deduct the 7 year tribulation timeline from the above date (Matt 24:29,30,36). The Tribulation is 7 prophetic years of 360 days each = 2520 days (Dan 9:27, Rev 13:5); May 14, 2028 - 2520 days = June 20, 2021.
The maximum time to the start of the Tribulation period = June 20, 2021.
The trigger to start the Tribulation will most probably be the age old issue; For when they (UN!) shall say "Peace and safety" (Two State Solution parting Israel), then sudden destruction (Tribulation) cometh upon them, as travail upon a woman with child; and they shall not escape." (1 Thes 5:3 KJV). God warns the world that "parting my land" will bring swift judgement (Joel 3:2).
Believers who are ready all the time between now and June 20, 2021 might have to wait up to a further 9 months ("as travail upon a woman with child") for the Rapture to take place - that's up to March 2022 max.
Sadly, the world will celebrate this "Peace and safety" covenant the day it is announced...but, to their doom!