When does apostasy begin? And, end?
What about Balaam?
Sampson?
Maybe I do not understand apostasy?
Some think it is only a desiring false teaching and living it...
Isn't apostasy is a falling away - departure?
apostasia, transliterated apostasy, is from apo - away from, and stao - I stand, so, "away from standing", that is, to depart from your location, departure.
In Classical Greek, this was the set meaning. Aristophanes, in his play "The Birds", used the word to describe the departure of two men to the bird city in the sky, as they planned their "apostasia".
By the time of the Septuagint, it had taken on the usage of "rebellion".
The only two places it appears in the NT are 2 Thessalonians 2 and Acts 21. The first references the end times, the second references the people's accusation against Paul, that he teaches departure from Moses.
Acts 21:21 KJV
And they are informed of thee, that thou teachest all the Jews which are among the Gentiles to
forsake Moses, saying that they ought not to circumcise their children, neither to walk after the customs.
When you look at the construction of the verse, you can see that "rebellion" doesn't fit, while "departure" does. "From Moses" You don't "rebel from", you "depart from", while you "rebel against".

The verb form is used a number of times, with a clear usage of "departing".
So then while there is LXX usage that points to rebellion against authority, the actual Biblical evidence points to departure from something, with the context needed to show more.
As for when it begins and ends, I'd have to answer it begins with the decision to leave. Ends? I don't know. When does "leaving" end?
Much love!