I believe that falling away (apostisia) of which Paul speaks has been underway for quite sometime now and is growing louder and stronger as time passes.
It would be my opinion, based on scriptures referenced, that we no longer need to wait for part 1, the falling away.
What is next is the revealing of the son of perdition.
I also believe that very shortly after he is revealed, the Bride will be taken. I'm thinking that time frame is very short.