I don't know about you, but my contract states I'm supposed to work X hours and includes a passage on how overtime is handled. The rest is common sense: That an additional, equivalent job can't possibly be done well.
Your employer pays for your (mental, in this case) energy.
I know accountants who work between 80 and 100 hours a week for 3 months every year. Is it miserable? Yes. Is it impossible to work that number of hours and turn out quality work? I don't think so.
Your employer pays for your (mental, in this case) energy.