In the US, managerial or supervisory roles (pretty much any job you'll get with an MBA) aren't eligible for OT pay. So your base salary is what you get paid regardless of how many hours per week you work.
I'm not sure how consistent that is in other countries though.
NJMike is right. I think from my taxation days, the definite rule was - if you manage 2 or more people, you are considered a manager - therefore, you are not qualified for overtime.
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