If this may contribute a little, here is how I go about my backups :
First,
is how I handle my snapshots.
(You can also see that my projects auto-save after 5 seconds of inactivity, so I don’t ever have to bother with a manual save per se.)
And as of the backups themselves, rather than having the operation linked to a manual save or to whenever I open and/or close a project, I use the “Back up Now” menu command.
Which I have as a button on my toolbar :
→ On an average day, I’ll do between 10 and 20 backups for a project.
These manual backups automatically end up in a folder on my desktop, named “Novel backups”.
Whenever I feel like I progressed enough to justify it, I copy the most recent backup to a thumb drive that is connected to my computer through a hub that has switches. (I usually do this when leaving the house for a while. Or whenever, like I said, I feel like my recent progress is worth it…) I switch it back off right after the file transfer. (No need to have it accessible all the time, if something one day goes wrong, might as well spare me the trouble of having my thumb drive messed up as well.)
And finally, as part of my routine, when the day is over, I upload the very last backup of the day (from my desktop backup folder “Novels backups”) of whatever projects I worked on since last upload to my cloud backup.
This or these backups (the local original copies) then go to a folder named “Archived”, located inside the “Novel backups” folder that is on my desktop.
I delete whatever other backups I cumulated during the day from the “Novels backups” folder.
Once or twice a month, I add the content of the “Archived” folder to an external SSD drive, and empty the “Archived” folder from my computer. (That external drive is dedicated to backups and storage, and is also disconnected until next time after the operation.)
So this way, I have a temporary backup on my thumb drive (short term protection), but also, and at all time, at least 2 other places where my real backups (the last one of each day’s work) can be recovered from, if needed.
To be in trouble, I would need :
- To lose/break/get my computer stolen ; and
- to lose/break/get my thumb drive stolen ; and
- to lose/break/get my SSD drive stolen ; and finally, on top of all that,
- some hacker to burn Google down to the ground.
All of which in a single day…
I feel pretty safe 
→ And none of that requiring much of my time to handle. (About 3 minutes at the end of each writing day.)