For all I care he can set them all down and line em up, then change his mind and set them on the other side, then move them again. But once he says he's set and a ship of the next higher PS (mine or his) is grabbed then they are locked.
Naturally if my opponent was messing with his TIE Swarm and the clock is already running then I'll let him know we're on the clock ad he needs to get his ships down (so I can get mine down).
Kind of like playing Orks in 40K. If you can't move 6 squads of 30 boyz each in under 10 minutes you need to play a different army. Likewise, if you can get 7 Ties down in 5 minutes you need to fly BroBots.