Best teacher I had in university offered "unlimited time on tests". Their tests were hard as hell but they were scheduled after the last class of the day and ran until like 10 at night. It worked out to like 5 hours of test time even if most people could complete the test in like ~1.5-2 hours.

The policy was essentially "you have until the teacher/TA needs to go home" and given everyone in university is always swamped with work they were generally willing to stick around and get their own work done until it got super late and even then, even if you were the last test taker they'd generally negotiate a final 10-20 minutes with heads up so you could do your best to wrap up even if you weren't done.

But generally the rule is ~2x test time. The extended test time accomodation is normally listed as "double time" in my experience even if profs were generally willing to give you more than 2x time if you were still making meaningful progress.

Yep. That's exactly what I did when I taught at the university level. Mind you, I was single then, and had no family responsibilities, and the school was small enough that I could ask for the last test slot of the day and always easily get it. But, it's excellent for everyone.

It's unfortunately not practical for every class to do when everyone's taking all of their finals in the same week. There will be inevitable scheduling collisions: hence the need for timed slots and individual exceptions at alternative times and locations. If you can think of a systemic solution to that, I'm all ears. (Yeah: get rid of final exams. In theory I like that idea, too. AI is kinda pushing educators in the opposite direction at the moment.)

This is a fantastic idea, as the exam becomes part of the teaching - if you sit there for 5 hours wishing you prepared your study better, that's an invaluable lesson.

I suspect the reason why it does not occur more commonly is simply because of the costs of running such a long exam.