How quick is time machine backup?
Much will depend on your infrastructure.
My TM backup route: 2019 MacBook Pro (macOS 11.1) - ethernet - router - NAS
My initial TM backup takes about 45 minutes for 85GB data and system.
Incremental daily backup takes about 10 minutes for 25GB of new and changed files.
If I was backing up to a drive attached directly to the MacBook, backups would be faster.
There's lots of chatter about making TM backups but not so much about restoring TM backups. Before proceeding you should thoroughly research the TM restore process. In my case, using Internet Recovery, a TM restore from NAS takes 45-50 minutes to the login screen.
When your initial TM backup is completed, you should check that it will restore but be aware the restore process initially completely erases the destination (internal) drive. This is a typical "Catch 22" situation because although rare, if your test restore fails after the destination drive is erased, everything is lost. That's why it's wise to hold a current backup of all your personal files on a separate drive. Alternatively you could explore a third party cloning software such as Carbon Copy Cloner or SuperDuper which can produce a bootable clone of your entire system, applications, personal settings and data. I use CCC as a complement to TM; it's very fast and accurate. CCC offers a fully functional 30 day trial which you could use to produce a bootable clone as insurance until you were sure your TM backups could be successfully restored. Don't store the bootable clone on the same drive as your TM backups.