I didn't want to pull the whole oven out of the cabinet & unplug it if I didn't have to, and I hit on the idea of setting the timer to its max, 9 hrs 55 min, so it would be busy counting down and maybe not allow the beeping to begin.
The first time I tried it it seemed to be working. It was down to 8 hours and a few minutes when I was getting ready to go to bed. So I re-upped it to the max and hit the hay.
At 9 hrs 11 min, there it went.
Seems A** A*****, the (likely anal-retentive) *** periodicals librarian who owned the house (and the stove) before, had the same problem back in 2000. I know, cuz she kept meticulous records. Upon retrieving the manual for this appliance from the stack she left, I found that she'd replaced the stovetop for some reason at one point, and that the blinking F1 had, after several phone calls for which she had date&time&name-of-person-talked-to notes, resulted in a replacement of the keypad, costing her around $130, after the 50% off of parts that she got under some warranty I don't have.
I guess it's good to have the medical history of all your appliances. I don't have to try to figure out its model # or search for its serial # or anything. I did think for a bit about trying to get along with just the microwave, or with rigging up some kind of switch so that I could boot up the oven when I wanted to cook, stay nearby to hit "stop" when it got to complaining, and shut 'er down afterwards.
But this is why the gods made credit cards. Right?
ADDENDUM: Turns out this problem is a chronic one for many an (unfortunate) Magic Chef owner. I may try some stop-gap fixes myself before shelling out for the repair (or part).