Fresh Big Sur installation stuck on “Less than a minute remaining” for hours

Start up your Mac in safe mode This may or may not allow the update process to complete

I have some additional thoughts to share. I suspect that the installation file has gotten corrupted during the download process and therefore will not complete the installation. I would drag the installation file to the Trash and empty it. Then do another download. Often times doing the download via Wi-Fi does not work. These are very large files and Wi-Fi is just too slow for them. I suggest that you connect to your modem with an Ethernet cable for the download. The download should take an hour or so, more or less and then another 45 minutes or so is required for the installation with several automatic restarts. The time remaining notices are very inaccurate, so don't take them literally. If you are unable to do a direct connection, then it may take several lengthy downloads to get a clean one that will install. Good luck.

I had the same issue and I just redid the download and started over. This time the one minute remaining was really 5 minutes but at least it finished..