My son goes to AF Rotc so I can only go based on his experience. I have to imagine all of the other Rotc are more or less the same. First you dont miss one day of school. Rotc classes are just another class during the day. I think he has two Rotc classes a week, does PT every other day around 630 in the morning and has one day of drill instruction which I think is included in the other days I have mentioned. So instead of having four classes a day, you have five classes a day. Any other activities are done after school hours and on the weekends. All AF cadets, assuming they are selected, go to AF Field Training (Alabama) the summer before Junior year and prior to that they attend a 2-3 day weekend event at a nearby AF base where they get the flavor of living on a base. In neither case, do you lose any school time. The only school time my son missed was when he had to go to Wright Patterson AF base to get medically checked in order to be a pilot.
Next, I dont have much knowledge about the medical field in relation to the military, but from what I read here, if your plan is to go to medical school, I would avoid Rotc. Once you graduate and commission, I dont think you can call a time out and attend medical school. You are going to have to serve for a minimum of four years or around 11 years if you are a pilot. I would imagine that after the four years and only if you qualify for their program, would they then send you medical school which you would then have to serve an additional number of years. The problem is that you wanting to go to medical school and the military need for you to go may not jibe. As someone else posted, the AF academy only send 1-2 kids to medical school every year. Are you going to risk your medical career on what the military wants. The military doesnt even need you as a doctor. There are people who go to college and medical school on their own dime and then apply to the military where they are commissioned.
As for what you will do, it all depends on what you want and what they want you to do. It also depends on your major. I dont know which branch you would want to serve in. Each one has it owns types of jobs so who knows what you would do