Doctors in their residency have notoriously awful hours, so bad that they had to legislation was crafted merely to cap the hours at a four-week average of 80 hours (meaning that, yes, they could work 3 one hundred hour weeks and one 20-hour week).
Also, you are expected to be active researching and publishing and studying for certification; figure another few hours a day outside of the hospital when you're not on call.
Nowadays, they have a new system, "Doctor's Watch", where the GP's from a certain area operate at night in rotation. It's a bit more official and less personal, but it does allow those not on rotation to get a proper night's sleep. Pretty sure they'd compensate that by working less hours during the day / week.