I think it depends on a couple of factors, mainly in the progress you make. If you are stuck 40 minutes without a clue, you should look for hints, however if you are slowly getting to something that seems the answer, you should keep trying. If I can not solve a problem in under an hour, I skip it and think about it while I do activities like walking, cooking, pooping :p, usually some hours after I stop thinking about the problem.

If after this I cannot solve it, it is clear that it is above my skills and the right thing is to look into the editorial to learn something new. If you cannot solve something with the skill you have, there is no point into investing extra time.