well, for example, buffalo will make a decision (acceptance, rejection, or wait-list) like an hour after you leave the interview day. But they won't let us know anything until December 1st.
However, they also told us (other schools as well) that if we don't get an acceptance by Dec 1st, it doesn't mean you won't get in, it just means it might still happen sometime after
I really don't like to think about post-interviews, its no longer in your hands