There is an entire forum devoted to clinical rotations. You are free to peruse there for your answers, but be aware that should you post a thread it will likely be moved as you are pre-med.
Short answer: depends. Depends on the rotation, the attending, the hospital, the residents, and you. Surgery hours tend to be long. Ambulatory tend to be short. Wards are long. As a student you may or may not be subject to ACGME rules (as of now such compliance is totally up to the schools to regulate. Many students are still doing 24-30 hour calls.) On surgery you may or may not be scrubbing in. If you scrub in you may or may not be only a retractor monkey. On the other hand, I was first assist on most surgeries in my third year, including a total hip and ex-lap for metastatic cancer multiple resection. On wards you will likely have patients assigned to you and have oversight of a resident. You will likely have inservice exams every rotation, have to do a presentation or two every month, and will also be studying for boards. All that in addition to hours that range anywhere from 8 - 24 hours per day or more. On a few rotations you may have the fortune of every weekend off, but likely you will be lucky to have one day off in seven.
Elective rotations are a different ballgame. If it is an audition rotation, you will be putting in the hours. I did away electives where I had homework, presentations, and weekly exams. I had others with every weekend off and easy peasy hours. Classes usually consist of weekly conferences that you will be expected to attend.
Your next questions will likely be geared toward what the heck I meant by some of the above. My pre-emptive answer to that is to worry about actually getting IN and getting TO third and fourth year. That is at least two years away and a lot can change between now and then. And like I stated above, also depends on where you go to school, the hospital, the attending, the residents, and you.
