From what I know, it highly depends on the program. For example IMED has weekly in-person meetings for ~2h + individual/small group research tasks outside of the classroom/lab space. In addition IMED has a mandatory component of 6 weeks during the Summer semester with clinical immersion.
UICOM has the M1 and M2 schedules posted on their website -
M1 & M2 Block Schedules - so you can take a peek at the sessions scheduled.
Individual concentrations also have their curricula described, e.g. for IMED:
Program Curriculum
Is it hard to balance? Sometimes yes, but it's 110% doable. However, when you're in a concentration the time spent on it isn't some busy work - you gain a lot of useful information and a ton of experience from it. In the example of IMED yes, you don't get as much time in summer in comparison to the regular track, but you automatically get a pre-planned clinical immersion which normally you would have to organize independently. If you ask me it's a win-win
🙂