Since I updated to High Sierra, I frequently get the "No Backups for x Days" notification. I used to be able to make this go away by turning off Time Machine in the System Preferences until I needed it, but there is no way to turn Time Machine off anymore. How can I get rid of these notifications?
I suggest you get TimeMachineEditor and set your backup schedule to once a week or some time period you find more suitable. This app overrides the hourly backup default schedule of Time Machine and lets you define time periods to prohibit backups.