My dad was a Surgeon, passed away now, and when he was junior registrar etc, he used to live on Hospital site, this was in the 60’s to early 70’s, where he did crazy hours, he was on call all the time, so he could do a 12 hour shift, head off to sleep, then get a call say after 2 hours sleep, then have deal with life or death situation etc, go back to sleep, then another 12 hour shift later in day, If remember correctly, in one year, he had just one weekend off. By the time me and my sister came along, he was climbing the ladder, so hours got a lot better, and in the end he was on 8-9 hours days generally, and he went on to become, an eminent surgeon in his field, and was one of the best in Europe if not the world.
He always said the brutal hours in his early career, were what trained him to become, the great surgeon he was, now i dont know the exact hours he worked early in his career, and once could look up if one wanted to, but I know they were brutal, compared to now, where they are much more regulated, which, is good, but he said, that there was something about the hours etc which gave better training,which doctors etc have lost with less hours. I personally think, there has to be a good balance work life balance, so really 10 hour max shift.