One thing my wife and I have run into is there are a lot of part time Doctors. My nephrologist only works every other week. Not sure if this is by her choice, or if that is how many hours the practice she is part of is willing to pay for. My wife's GP only works 3 days a week.
Many times they work at different places on different days.
My brother is dealing with many doctors currently and they are all never in the same office on the same day so he ends up with multiple appoints on different days. He is terminal and does not want to drive or deal with going into the city so that limits him even though we are a mile for a major hospital. Many times he did go into the city they would do blood work and say he cant get treatment so its just not worth it.
Anyway many docs work a few days at the hospital, a few days in a local office and then a few days in an office that is in the city.
This is not unusual from what I see.
I know one GP who does not work till noon and works 3.5 days a week.
That 5th day is often doing paper work or writing up things for court cases etc..
So even though he does not have office hours he is still working and often working at night or weekends on paperwork.
Also has to work on Saturday a month in the hospital. And of course if one of his patients has an emergency he needs to be able to respond. He is in a small town so he has to be responsive to folks.
Without a doubt its over 40 hours a week and much of that time is not really paid.
After many years in private practice they are finally at a point where they are comfortable, but at that point you are getting ready to retire.
In general I think GPs are grossly underpaid, again, not just in the US.
If you want to make money you really need to be a specialist, so for many that is they way to go instead of GP.