Congrats on the II to Duke,
@kjj17!! I have done 5 MMIs, so I've definitely seen some variation between schools. Some of the time, you will have a conversation with the interviewer for the full 6-10 minutes or however long they give you; at other schools, after you give them your initial opinion, they thank you and ask you to leave the room and wait outside for the last half of the time limit. I prefer the former, but be prepared for both!
My experience with MMIs has been largely positive. I enjoy meeting people, so I didn't mind that aspect, whereas I know some introverts who hate having to bounce back and forth between different interviewers and have to give 8 first impressions in the span of an hour or so. I guess I approached it optimistically, like each new station was a chance to impress someone else or get someone else excited about advocating for me on the admissions committee. Who knows if that's actually how it works, but it made me energized and eager to perform my best each time. My general approach went something like...
Outside the room:
Read the prompt several times, mentally plan or physically write down thoughts as to what I want to say (note: I never looked at my notes inside the room -- it just helped to organize things a bit, since adrenaline and nerves can make your brain feel scattered), tried to imagine both sides of the argument so that I could address the issue from multiple angles
Once we were given the cue:
1) Knock
2) Open the door and introduce myself
3) Sit down when directed to do so
4) When they inevitably ask if I had time to read the prompt, say yes before beginning
5) Basically say, "Here are the two sides that I am seeing..."
6) Conclude my ~2 minute spiel with what side I am leaning towards and why, and (if applicable) what steps I would take if faced with this situation
7) Follow their lead, either by having a conversation about these topics or by leaving the room if I am asked to do so
I did my best to give genuine responses, and if they said something that I hadn't thought of, respond in a very humble and receptive way -- "Oh, I hadn't thought of that! That's an excellent point. I should have considered that in my initial argument, but now that it's brought to my attention, I might change my perspective to include x, y, or z." -- or something, depending on the circumstance. I'm not sure if sticking to my guns would have been better, but I wanted to genuinely show that I can learn from hearing other peoples' opinions and that my ideas aren't inflexible. But like I said, each circumstance is totally different and it's so hard to generalize. Basically, I just said what I thought and felt in a hopefully polite and articulate way.
I have no idea if this helped hahah I sort of just typed a stream of consciousness about my MMI experiences, but maybe you can glean something useful from it... If not, I'm really sorry hahaha. But good luck on your interview regardless! You'll do great!!
I guess I just need to suck it up, make some, but bundle the rest up in holiday gift baggies.... 
