Microsoft have generously provided a pop-up just before the scheduled update starts. You'll have 30min to work out which option actually cancels and this time the X will follow guidelines and cancel the cancel option. For added convenience they'll leave the scheduled time just when you expect it, while you're soundly asleep between 4 and 5 am. Don't worry, the pc will wake up for it, even if they have to hack your settings and BIOS.
Have I said ”cnuts” yet?