The 3rd year rotations at my school were done mostly in podiatrist offices and hospitals near the school, averaging 40-50 hours per week.
As for the 4th year, part of the 4th year may be spent at or near your school for classes/rotations, but to my knowledge all schools' 4th year students spend at least several months on rotations at your choice of residency programs. At my school we spend 11 of the 12 months of the 4th year at outside rotations at various residency programs. The workload/hours depends on where you choose to go. Most of the programs I've attended are 40-50 hours per week without weekend call, but I've had rotations with a night or two of call per month and I had one rotation with a fair amount of weekend work (ER). However, I have spoken to classmates that rotated at programs with much longer hours. In addition, my school does have online/teleconference evening classes throughout the 4th year. Most of the students from the other schools that I've talked to haven't had this while on outside rotations during the 4th year.