I'm guessing when others give up their position. It depends where you stand in the reserve list as well, I've heard some got in before the school year started but I've also heard some got in half way through a school year.... U may call the school and find out if there are others in front of you. But best to have a back up school for now. All the best.
From past experience they can probably tell you how long it's likely to take. But as previously said the even the school itself wouldn't be able to tell after the confirmation deadline and by then they go down the reserve list.