Congrats on the interview--it's a VERY relaxed day.
When you get there at 9, you'll be chillin in the waiting room with the other interviewees. You'll then get a short introduction, after which the interviews will start.
Basically, the interview comes to the room, calls your name, and you go off to a different room for the interview. When you're done, it's back to the waiting room, and then repeat. There are supposed to be two interviews (one with faculty, one with student); however, if there is a large score discrepancy between the two of them, you will have a third. Also, during the waiting room time, there are students present to answer questions.
After this, you will have the tour/lunch time. If i remember correctly, the tour is broken up into two components, with lunch sometime in between. Lunch is pretty good--it's at their cafeteria--and you have a $7 meal ticket i believe.
Good luck, and have fun!