I also have a backup macro, what I do is keep a list of all created backups and delete the oldest one (for me the 100th but could be less or more).
In the attached macro change the directory accordingly (don't forget the export macros action) and run the empty trigger (it will delete all backups in that directory though).
You can configure number of backups to keep and time between backups.
To change the number of backups change the number of iterations in the very last loop and to change time between backups change the interval trigger.