The day either starts or ends with two interviews depending on whether you are a morning interviewee or afternoon interviewee. Between the morning group and afternoon groups sets of interviews, there are two presentations for all interviewees over a light lunch in the late morning (one by admissions/faculty and one by students) followed by a very short tour by students.
The interviews are scheduled for about 30 to 40 minutes. They are relaxed/informal like everyone else says, but it is hard not to be somewhat nervous before you get through your interviews. It is a nice place with nice people. Enjoy the interview process and try to get as much as you can out of it. Ask questions whenever you want throughout the day. The experience was definitely a positive one.