"Checking for updates" can take a very long time if the PC is well out of date, but I haven't personally had it take more than a couple of hours on a slow machine.
That is indeed the hazard -- getting short on patience.
I've been through all the fixes listed in this article:
https://www.winhelp.us/reinstall-windows-update.html
It got my flagship desktop back on track permanently. My laptop was fine for a month, and then WU took another dump.
You'll find a thread in this forum about sequentially installing independent downloads of a KB____612 (new WU Client update) and a KB____739 (seemingly unrelated graphics patch). That seemed to work for me.
But -- patience. I had to disconfigure my laptop's sleep and hibernate temporarily. The "checking for updates" took maybe three hours. After that, no problem at all.
Also, what happens with some of the most aggressive fixes, particularly if they don't work, WU loses track of all the updates previously installed, especially if you purged the distribution cache (which sometimes helps, actually). So "checking for updates" takes a lot of time to restore the list of installed updates.
WSUS Offline is a marvelous utility to circumvent WU and simply turn it off. It will keep you current on all updates, but it will not make it possible for WU to show them in the "previously-installed" list.
So if you want to eliminate the hassle of WU running in the background here and there to hog some clock-cycles, you would simply pick the "unrecommended" option of turning it off (disabling the WU service at startup), and schedule an hour or so monthly to led WSUS Offline install updates. The menus on the program are just detailed enough to allow you to selectively do updates for Windows or Office, download Framework or C++ libraries as needed, and so on.
I'd rather just open a WU with a synched and accurate list.