Thanks for all the kind words, everyone.
I will have a checked bag (it's hard, at least for me, to spend four weeks in mainland China without one...) so it looks like I'll need to arrive about 90 minutes early. That's not quite as bad as I had been led to expect, even if it's longer than I would have liked.
NRT-SEA gets in at 7:35am PST, so if DL's computers really acknowledge status changes at midnight EST, that should be plenty of time for them.
Fingers crossed for the upgrade... the seat map looks pretty good, with 14 F seats open and many preferred Y seats open, suggesting a medallion-light flight. But we all know how reliable the seat map is.