I think they normally only run once per day and at night.
If you prefer to have more control over your backups, you can also setup a cron task and use the ‘mysqldump’ command to run the backup from your own script outside of the ERPNext functions.
You can see examples of it in the scripts I have posted in another thread dedicated to a complete backup system. Even if you don’t want to use all of the information there, you will at least find many useful commands that may help you. See here: