[Jan_Sobieski]

Here is a critical verse to understanding when the Rapture could occur…

2 Thessalonians 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; 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.

[MHGinTN]

A better rendering of The Apostasia is The Departure or the departing. Here is the Geneva Bible rendering:

3 Let no man deceive you by any means: for that day shall not come, except there come a departing first, and that that man of sin be disclosed, even the son of perdition.

The 'that day' in the Greek refers back to the day of the Lord. And the chapter begins by focusing the reader on the gathering unto Him that we should not be deceived over because the departure comes 'proton' / first before the man of sin who is the bane of the tribulation years can emerge.

The first several English translation Bible from the Greek rendered apostasi as only departure or departing.