Comparing MS3 schedules from 2 different locations, it seems that it can vary quite a bit. In general, surgical/obgyn rotations have longer hours whereas psych/fp have shorter hours.
Psych: location 1 40 hrs/wk, location 2<<40 hrs/wk
IM: Location 1 50 hrs/wk, location 2 60 hrs/wk
Gen Surg: Location 1 100 hrs/wk Location 2 >>100 hrs/wk
Peds: Location 1 40 hrs/wk Location 2 50 hrs/wk
OBGYN: Location 1 >>100 hrs/wk Location 2 60 hrs/wk
In the end, it really depends on how much call you are required to take and how well you want to do in the rotation. Many of the university programs have longer hours than community programs, though again this can vary.
Hope this helps.