I'll be blunt. Undergrad and med school are very easy compared to surgery residnecy and fellowship. They will be the hardest things you ever do.
During general surgery, I averaged about 90 hours per week. However, some weeks I only worked 50-60 hours and I worked as much as 150 hours in one week. It all depends on the rotation that you are on and your seniority.
As a junior general surgery resident, I woke up at 4 am and was at the hospital by 5 am. I got home on average around 7-8 pm and was asleep by 9-10 pm. I was averaging 6 hours of sleep on non-call days.
As a senior general surgery resident, I woke up at 6 am and was at the hospital by 6:30-6:45 am. I went home around 6-7 pm and usually got to bed about 9-10 pm. I was averaging about 7-8 hours of sleep. However, I was on at home call every day, so I was getting an average of 4-5 pages per night. So, my sleep was very broken sleep.
As a fellow, I average about 90-100 hours per week. I wake up at 5:30 and get in the hospital around 6-6:30 am. I'm usually home by 7-8pm. I go to sleep around 10pm. On most rotations, I'm on at home call q1 or q2. So, most nights I have broken sleep from a lot of pages. I have one rotation which does in house call q5.