Holycow, both possibilities are possible, one could only speculate. I am not aware of any ATR crews on 4/4, but there are a few on the A320.
There is no set period of time that you must wait, you will make a request through your contractor whenever you like, then wait for a response from the airline.
There are no guarantees here, there is no seniority here, if you do a good job and the company likes you, almost anything is possible.
Cheers, D.L.