Can't speak for Prime, but I use OCCT for an hour to test for stability. After that, I just carry on with the normal games and programs and make sure everything runs OK.
Both synthetic stability tests and real-world apps should be used to test for extra assurance. I've done Orthos (which I believe is based off of Prime95) overnight before for 8 hours, but I think it's to discover underlying problems you might not otherwise see playing games. I've had settings that passed 5 hours, then failed, and later, I had problems booting. Gaming might not have detected this.
But yea, OCCT is more intense, quick and dirty (1 hour is usually enough), so I prefer to use that.