It really depends on the school....
Most start official classes at the end of August (HBS starts in Sept) and most have some sort of orientation in August (HBS has theirs in Sept). A lot of the schools have pre-orientation math or analytics bootcamps as well, usually sometime in August. Wharton, for example, is a little different, and has like a month-long required "pre-term" for all students, while Stern has a 2 month "summer start" program that starts in July, but isn't open to everyone, and Tuck has "math camp" which I think goes on in August for a week, but again, isn't open to everyone. But whether you're talking about pre-orientation bootcamps or orientation, for the most part, these are full-day, all-day affairs with social events in the evenings, so you can't also expect to go to work on those days.
So as you can see, it is very different across the board. I don't know about healthcare, though, that's a really good question.