I think it is a lot more common in chem and bio for the sort of reasons you say. You have to work on the schedule of the experiment, which isn't always conveniently aligned with an 8-5, M-F schedule. I did theoretical physics at Caltech and there was no expectation of this sort from the profs. Lots of my friends in chem & bio (and to a lesser degree experimental physics) worked kinda crazy schedules. Even in those departments, though, some profs were known to be slave drivers and some were more relaxed.