So my thought with the time based pruning is that you can keep a backup that’s X days old.
Let’s say you keep 2 weeks. If there have been no problems with an image after 2 weeks of an update, you’re probably good to go. If you have an issue during those 2 weeks, you can return to and image within those 2 weeks. If you’ve had no problems after 2 weeks, it’s probably stable.
Adjust 2 weeks to whatever you’re comfortable with.