Tempted to make this the update where I finally switch to Open Core.
Think I did right when skipped FileVault and directly change to the boot Mac OS drive, works goodTo anyone on the edge of the pool, waiting for other's reaction to the update: jump right in! The water's warm!
After the download, I think it was about 15-20 min. From the start of the process after the download, there is a minute warning that it will restart. It restarts into the update process. There is another restart that brings you into the Clover bootloader, and you go into the preboot. Then finally another restart, and you go into the filevault.
There is a wildly inaccurate countdown timer, that ticks down minute by every 2 minutes (it seems), but it eventually gets there. 15-20 min of sheer terror, but I emerged on the other side. I did another restart just to make sure it boots into my system drive.
Heed all the warnings in the original post. Backup using CCC, make sure all your kexts are in your EFI and are up to date.