A lot of good points above. I’ve worked 50h a week and after 2 months was about ready to crack.
I’ve also worked 50h a week for 6 months and been fine. All depends on the stress levels for those hours.
In my experience, most jobs never have completely empty queue (unless you are near the bottom and being spit fed chunks of work). Especially as you go up in a company it’s all about picking the key parts or tasks to work in and knowing when to stop.