I don't recall 100% but interview day was around 6-7 hours long. It's a group event but the MMI themselves are one-on-one (Zoom breakout rooms). Half of the interviewees do the MMI before lunch, half after. Most of it is typical interview day stuff like Dean's Welcome, Curriculum Overview, Financial Aid, Student Affairs, Q&A, etc.
The MMI questions are less stressful than most of the ones that you'll find online but we can't discuss the specifics of the questions (I think signing up for the interview day was an NDA in and of itself and the admissions office does read through our SDN threads). As far as I remember, there are 8 MMI stations. You get 2 minutes to read/think and 6 minutes to respond.