One MemTest86 pass is enough.

Yes, run it. One full pass will catch most serious errors.

If you’ve got a brand-new kit from a reputable brand and just want to make sure it’s not dead-on-arrival, a single pass is all you need. It’ll take anywhere from 30–90 minutes depending on your capacity and speed. That’s enough to catch obvious fails—bad modules, timings off, that sort of thing.

If you’re overclocking, mixing sticks, or already seeing crashes, let it run overnight. That’s belt-and-suspenders territory. But for a standard install, one pass gives you reasonable confidence.

Better to catch a bad stick now than to chase phantom crashes later.