Dear Restart Dialog,
I hate you.
If you want to temporarily disable this popup message and delay rebooting, you can go about it one of two ways. I’m a command line junkie, so I just type this into a command prompt (make sure you use the quotes)
Or you can open Control Panel \ Administrative Tools \ Services and click Stop on automatic updates.
Do not disable the automatic updates service, just stop it. The next time you start up your computer, it will restart.
Note: If you open the Automatic Updates icon in Control Panel, it will automatically restart the service, which will make the dialog start popping up again.