it's not powered by norms. In the US, if you want to employ someone more than 40 hours you have to give them extra overtime pay. It's called the Fair Labor Standards Act and it was passed in 1938
It's easy to get around that; just switch your employees to a salaried arrangement, and now you're exempt from shelling out for overtime pay.
Give the employees enough work such that they have to work on weekends... and... done.
Unless you are exempt. Guess what profession tends to be considered exempt?
If you are a SWE, you don't get paid overtime for working that incident on the weekend or going over 40 hours in a week. The only reason you work five days a week is tradition.