But that is how certain exams are done right now. Though it's usually 30 minutes including overhead. It's not something you can do in classes with multiple hundred students, but it's certainly done at scale.

I was the PhD student in the room in dozens of these exams, and I toke some of them myself. But that was for classes with a bit less than 40 to maybe 60-80 students. The load for the larger ones was shared among professors, if I remember correctly. But it was certainly the case that a single professor spent 1-2 days doing nothing else but these exams.

And it was 1 professor and 1 PhD students, and those don't count. They essentially grow on trees and are always available, if you need some.