I also have this issue. Stuck on “less than one minute” for hours. Reboot only leads me back to the install process which then gets stuck again. Booting into safe mode doesn’t work either, goes into a loop as described before. Managed to boot into recovery mode, tried reinstalling Big Sur from there, install process too over an hour and... got stuck at “less than a minute remaining”. This is my work machine, I’m a remote worker, I rely on my equipment. Only reason I even attempted the upgrade was because Docker was kept asking me to.
After 15 years of MBP ownership and loyally sticking with Apple and OSX I’m at the end of my rope, company ain’t what it used to be. This is a very serious issue for the users that have and this thread has no meaningful response, just your standard help desk “have you tried rebooting”.
Expecting to get some sort of official reply here.