Here's what happened in my interview:
Two students, both MS2s, gave the demonstration. One played the role of patient, the other doc. They talked about a possible scenario and then the "doc" student performed OMM on the "patient" student and explained why and how he did each manipulation. You sit around and stare and if you have any questions, you ask them. It's not interactive- you don't get to "do" OMM.
My demonstration lasted about 15 mins.
Dr_sax