Update (apologies for the delay): Rolling back last week's latest "security" update put her to right. No problems since, and render times are back to normal. I hadn't changed anything beyond poses and camera angle in the saved scene, nor had I added or removed anything, so it was scarily odd that all the sudden the render times doubled. The only thing that could explain it was the update and subsequent reboot.
> Specs are simple and somewhat generic for 2021: Core i7 10th-Gen, NVIDIA 2070 GTX, 32GB RAM.
> I checked the video driver(and figured that maybe an update was in order to match the patch), but it was the same as always. In my lazy dotage, I default to the "GeForce Experience" handler and let it do the work. I'm certain though that something didn't sit well with the video driver; I've been using the "Game Ready" driver variant, though "Studio" would likely be the better version. I may tinker with that this week.
Otherwise, rolling back the update did the trick.