Is a 40 hour work week normal?

[Whack-a-Mole]

I asked something similar (I think) a few months ago. Well, not exactly the same but it got into how work time is counted per week (or whatever). It did not answer how many people work a 40 hour work week.

Interesting answers though and it seems it can get complex:

Overtime pay for hourly workers...is it 40 hours per week or can an employer mess with the calculation (60 hours one week, 0 hours the next week)?

The title basically lays it out. Some workers, such as oil rig divers, may need to work for 100% of the time being stuck a few hundred feet under water. But, then they are given a month (or more) off. If they are hourly employees do they get overtime for the way more than 40 hours per week they work while on the job or can the employer say that, over some time like a month, they are working less than 40 hours per week?