Hmm, it took me only 74 minutes to get to the desktops. Once there, I had to do the user accounts, and that was done in about 13 minutes tops. There was no start, stop, regression, start again, (download) progression was smooth and straightforward, (as was the actual install).
Could be that removal of almost all user files sped things up as Windows.old is 25.1 GB but the newest live version 1709 is 17.1 GB. At 30 minutes = 17%, but 74 minutes was 100%, with only two restarts required. Was finished at 87 minutes.
Did not uninstall Avast before starting. No glitches so far. Removed user files totaled 11.3 GB.
Once I am satisfied all is working as it should, Windows.old will be removed, saving me 25.1 GB disk space.
[EDIT:] Fixed ambiguous statements to reflect the difference between file download and actual install.