Comment by bluGill

Every interview I know is severely time limited. I don't care if you can solve the problem, so long as your are clearly making progress and have proven you could solve the problem if given longer.

Now I give you problems I expect to take 20 minutes if you have never seen them before so you should at least solve 1. I have more than once realized someone was stuck on the wrong track and redirection efforts were not getting them to a good track so I switched to a different problem which they were then able to solve. I've also stopped people when they have 6 of 10 tests passing because it is clear they could get the rest passing but I wouldn't learn anything more so it wasn't worth wasting their time.

In the real world I'm going to give people complex problems that will take days to solve.