1) It depends on the school. I know University of Alabama Birmingham makes their decision about the interview candidate on the interview day. Thus, later interviews will be competing for fewer slots. I'm not sure how many other schools do this, and UAB might be the only one.
Most schools write down all of the details in the interview so that they can remember you on December 1st. In this case, a later interview that is still pre-December 1st shouldn't be a problem.