Sorry for the delay, but you still have one day to prepare.
The interview format is three or four rooms with a small group of interviewers. You either interview in the am or pm and tour around the rest of the time.
Basically you enter a small room with 4 or 5 or so faculty in it. They are pretty friendly and ask you the typical interview questions. You rotate around to the other 3 or 4 rooms and interview.
Tip for group interviews: Look around and talk to everybody when you respond to a question. I always liked interviewing in a group because you aren't just sitting there staring at one person and having awkward moments of silence. If one person asks you a question, everyone is interested in the answer. So loosen up and speak to everybody in the room. They are all interested.