Its been a little while since my interview but here is what I remember. If you want to go on the tour, I think you have to be there at 8 or 9. Once you go in, they give you a name tag and a parking pass so you won't get a ticket. Then Dr. Brace, the associate dean for academics gives a small talk in a classroom about numbers and the interview process. The tour happens and I feel it was pretty valuable.
There is a room where you can hang out before the actual interview. There is breakfast food there in the morning and lunch in the afternoon. Professors that aren't interviewing that day come in and out of the room and talk to prospective students about the process and school. There are also usually current students there.
The actual interview has 3 professors seated at a table across from you (these groups change from day to day). They have your file in front of them and they ask you questions based on that. Sometimes the questions are out there, some are pretty tame, and it all depends on your interviewers. They last about 15 minutes. If you have any questions, I would be happy to answer them.