Read the Interview Feedback, cuz it's really helpful.
The day lasted from about 8:30am (but get there early) until 2pm.
The directions to the entrance were not clear at all, so as long as you get in somehow to the admissions floor, even if you have to go through the dental clinic entrance, it's all good. When I went, NONE of the interviewees went through the right entrance. Kristin from admissions could tell, since none of us came in with the name tags that were waiting for us at the RIGHT entrance. =P
They don't provide any breakfast, so eat before you go! I think my past experiences with Pacific spoiled me, so I totally thought Harvard was going to provide something before the interviews. They do provide lunch, which was nice.
Mine was like a real interview. They don't try to make it easy, or hard. Just standard, even though it's open file. So know what you're going to say for questions like "What's one of your greatest weaknesses?" You have two people interview you, and they're each for 45 minutes. Make sure to go with questions prepared.
Harvard requires a research project during the 4 years, so have a topic in mind that's of interest when you go in. They'll want to know if you're okay with the research, since most people aren't.
Ask about their clinical program. It's the polar opposite of Pacific, so that's something you'll want to ask about if that's something you're concerned with.
Congratulations on your interview! Have fun and enjoy it.