Hello Jay,
I just had my interview about a week ago. I was in the morning session so right around 8:00am, a faculty member approached our group and called a name, bringing one candidate back. There wasn't any sort of prep for the day. The interviews are one-on-one and last between 15-20 minutes-ish. I guess each interviewer is different. My interviewer (a lady) was quite vague and just asked me to expand on my application. Every question was essentially, "Can you tell me more about, *this*." The other interviewer apparently just went through a checklist of questions without any small talk, but the candidates all said he was very relaxed.
If you happen to get the same lady that interviewed me, definitely be ready to defend OMM and how it can be incorporated into your preferred field of medicine. Advocate for OMM. It wasn't that bad! Just relax. 🙂