It took a few attempts to get it to work. It wouldn’t work when I set it for 6 hours AND when idle for at least 10 minutes. When I changed it to 6 hours OR when idle for at least 10 minutes then it worked. Now that I have it working, it has worked flawlessly. I check now and again to make sure it is backing up and it is. My laptop slowed a lot during backups so the default every hour in TimeMachine was a pain. Now I have it every 6 hours and it works for me.