The day ends about 2, and no, the interview is not stressful. Keep in mind, that the interview is "open-file", so the interviewer will have you grades, MCAT scores, etc. in front of him or her. That could be a little intimidating. What's helpful to remember is that the interviewer is your advocate: it's in your best interest to just "sell yourself" and openly explain any discrepancies (grades, etc). Hope this helps.
Mr. Reses is right on. One very relaxed one on one interview. View it as a get to know you time that you can really take advantage of and show your stuff. And definitely voice your opinion on anything funny in your file. I had one bad semester, and my interviewer was great about it. She had me explain it exactly how she would present it to the committee if asked. Great school.