So far I haven't seen a lot of specifics. The short answer for time is about a day for me.*
I am not the authority on interviewing but I have had experience interviewing in multiple formats, including several medical schools and I got accepted so maybe sharing my process would help you. When interview season was getting going I made sure I had at least one reliable suit combo with a couple shirts and ties that fit well and were relatively in style. I generally do not use white shirts for interviews because I feel they are overused and a conservative color choice outside white worked better for my confidence and "standing out" visually. (If you are female, my main advice would be to not overdo the makeup and wear walkable heels is you choose heels). Then I made sure I had a cheap but professional headshot for those interviews that wanted a picture of you.
When it came to interview prep itself I would just google lists of medical school interview questions and practice them out loud with another person. They don't need to be memorized or contrived, but if you have actually thought of the majority of topics they could ask, you will probably feel more comfortable giving similar answers in the interview. A key to this is practicing out loud! Multiple times I thought my answer was good in my head until it sounded like bull**** or I stumbled over it badly out loud (time varies based on how well-prepped you are). I also usually did very basic research on some current major political and healthcare topics just so I could have a decently reasonable discussion and ask appropriate questions should they come up - don't spend too much time delving into intricacies, just know things that have happened recently (30 minutes tops). Once I felt comfortable with questions, I would spend about an hour and dig through the school's website again to find anything they were really proud of and anything I could ask questions about when they inevitably ask "do you have any questions".
My other big step was checking out the area as best as I could. If I traveled, I would try to go to campus the night before and see if I could find the entrance, or better still, the rooms I would be going to. It made me more confident to know the basic traffic flow and the way to the interview the next day. Finally, I would prep my outfit like ironing and getting accessories out, making sure toiletries were good, drinking an extra bottle of water, etc. Set a few alarms and have someone call you if you are not sure you will get up. If you are alone and traveling hotel staff have often been super helpful in this regard. Eat breakfast and have coffee or whatever your normal routine is. Don't do more question prep, you'll freak yourself out. Leave a little extra time to get ready and get to the interview. Don't forget ID. I usually brought my own folder and pad to take notes - sometimes you get this there but I always felt better bringing it. And a huge one that I noticed a lot of people would get caught up in - turn off your phone!
* This only refers to preparing for questions and does not include accommodations, dress, investigating the location, etc.