Interesting topic.
Depends on the build. But I stand behind a reputation of building bullet-proof PC's, and to verify they'll do that I run OCCT's series of tests.
I voted on your sarcastic first option, though it doesn't do a good job of explaining what I do and why I do it...
Some folks take stability seriously some don't (until it's an issue and they're on here pissed their system keeps BSOD'ing and can't figure it out...). I like to find a happy medium of testing and real-world use. If your system is stable for what you do, then it's stable for what you do and that's all.
I'm not saying OCCT is the end-all for stress tests...but for me it's a solid suite of tests that get the job done and have for years.
I don't use Prime or IBT, though sometimes I'll expand and use Aida64, Intel XTU, Asus ROG Realbench, etc. Frankly though, that's more depending on the system and situation. 95% of my situations, OCCT does it all and allows me to vet out instabilities.
If a system is stock, I'll still run it to see how it can cope with heavier than normal loads...
If a system is OC'd, then obviously stability should be tested so that's what it get's used for!
For how long it takes, depends on the response from the first test...if the temps are good and OC is stable on the first CPU test, then move onto GPU, then PSU. If all pass...then we're good...if not then it's time to adjust and retest. Some folks get away with not testing stability much or very long, I've been bitten and I'd rather take the time to do it right by methods I've honed by building and overclocking for almost 2 decades now. It works for me, and that's all that really matters in the end. My systems are stable, my customers are very happy and overly willing to pay me extra to make sure their systems are stable.
Onto timeframe, I start with 1-hour tests. That's long enough to have a consistent heat-soak and time for things to fluxuate in voltage, temps, and stress levels. If it is stable there, I'll run another one overnight that could range from 3-8 hours depending on how the system responded from the initial test. If all that is passed, then it's time to do what the system was built for...usually gaming or rendering, heavy multitasking, etc. The best stress test in the end is using your system for what you intended...but that's not always the most helpful when issues crop up, nor is it ever good timing. So if we can reduce the likelihood of BSOD's and crashes when merely using the PC, why not test stability?
