I'm not really sure exactly how it works but I think once May comes around the schools have the option of rescinding your acceptance if you have multiple deposits. SO if you get into your top choice (school A), you should accept, put your deposit down, then call school B and withdraw. Plus you have to think about the fact that schools ask for more deposits the later it gets. That means if you have deposits at multiple schools, you will have to put down an additional deposit at all of those schools if you want to keep your spots. Come May, I would think each school would give you a call and allow you a few days or even a week to make your final decision.
Again, some of this I have read, some is speculation. I would check the AADSAS or ADEA website for more info. 👍