Do not stress at all about your interview. It was one of the easiest interviews I have gone to so far, and the interviewers are very nice.
Here is a link to the question that they can ask.
Admissions Alumni Parent Program
Also, the interview lasts anywhere from 15 minutes up to 45 minutes.
Funny story with my interview. I had my interview the Monday after Halloween (which was a Saturday) Halloween night I went out to a frat party with some of my friends that go there, and we hung out with a bunch of people for the night. Come Monday, my interviewer comes to get me in the reception area, and it was one of the people I ended up hanging out with on Halloween!