3 hours for us as well. When you start doing graduate level work, a problem could easily last over an hour. And many people will have false starts before they figure it out.

It's not a problem with homework assignments as they have multiple days to finish.

So the professor has to decide between poor data with high variance, or good data with lower variance.

> I'm pretty sure that having more time would not have helped the weaker students get through the Quantum Mechanics exam.

Funny you mention that. When I did my (undergrad) QM II exam, I likely got the highest score, and I'm sure my score was below 40%.

There just wasn't enough time.