I have a rarely used system in a rarely used, spare, basement bedroom. Every few months, if I happen to think about it, I will attempt to get it current. So I'll fire it up then walk away knowing it will take some time.
The problem is, the darn thing will go to sleep before it has finished updating. So I have to start the process again and maybe again - unless I sit there and wiggle the mouse or press a key every so often.
I will say this though. When it finally finishes, it is current. That is, Windows Update worked without issues - again, just as it has every other time - at least for me. :)