Depends on CPU but I can't see a reason to run it that long with high temps.Is it safe to leave this running over night with the shut off temp at 90c?
Unless you are in some competition. 1 -2 hours of OCCT or any other test that loads system to full is enough. As soon as temperatures are stable , not much else can influence tests. As far as I'm concerned, those tests are for troubleshooting only. If you have a suspected HW problem it would show.