When he returns to the floor. But in this case I suppose when there is no longer a try - when the subsequent tap started?? Unless they can levitate this would be the only sitch I can think of where a try would end before he returned to the floor. That's why I think a ref could say it was an alley oop pass and not an attempt.

4-1-1 says when released the ball "on a try". In this sitch it is no longer a try or could be argued it never was. That's my story and I'm stickin to it.