During the first two years, our class hours varied from 3-8 per day, like most of the others. It depended on the block and the day of the week. There were more class hours during the second year.
HOwever, by the second year, class attendance was less than 20%. This is something that I don't think most applicants realize...that at many schools, the majority of students don't attend every class. Everyone has their own learning style, and many people skip class to study on their own.
Hours vary GREATLY in the 3rd and 4th years. Depends on your rotation and the expectations of students at your school. At my school, students are expected to see their patients and have a note written before the intern gets to the patient. We also take overnight call and usually work a full day post call. So, depending on the service, I have arrived at the hospital as early as 4:00 am (and to think I used to think an 8:00am class was early!) and stay til 8 pm (this was the longest non-call day hours I had)