I'd go ahead and pull the appropriate fuse rather than the battery cable. That will avoid resetting anything else that depends upon unswitched power. I don't know how long certain items (e.g., power seat positions) are held when there's no battery available at all.
Only pull the one for "Multimedia". It's a 15A fuse.
I pulled the fuse (fortunately, I'd read the owner's manual and knew there was a fuse puller under the hood -- those things are tiny
). I let it sit for a few minutes, so the electrons had a chance to run out
, put the fuse back, and voila, the clock was there again. The GPS hadn't lost the satellite info, either.
Thanks very much for your help!
P.S. Man, this car has a lot of fuses... I was glad for the chart on the cover (and in the manual).