This is how I normally use Timeshift. Once installed, I set it up using the 'rsync' option and use my '/home' partition which fills most of the drive. Depending on how big your drive is may determine how many snapshots you want to keep. I set this to 5 but you could drop this to 3. Then I take a snapshot and let it do its thing.
Now for the caveats. I had a failed upgrade from Devuan 3.1.1 to Devuan 4.0. I tried to use the restore commands at boot time:
sudo timeshift --restore
to start the process off but I had problems in that 'var' was too big. I decided I would try to copy everything in my /home folder to an external drive - and this is where you need to be careful. In the past I did not rely so much on Timeshift, just did straight backups of /home contents (including hidden folders - Ctrl+ H if they are not showing) and copying and pasting to external HD's formatted to NTFS - if you do this with a Timeshift folder it won't work as it looks for the format of the installation used, Ext4 - so if ever you are going to use Timeshift to an external drive, you may not want to use the entire drive for Timeshift, then you should shrink the NTFS drive and create an Ext4 Partition. You have been warned!