How can I disable the "no backup in x days" from TimeMachine? (Updated answer choice for High Sierra. See the old answer if you are still on Yosemite)

I'm running OS X Yosemite, and I want to disable the notifications from Time Machine. I rarely do a hard-drive backup because all of my essential files are in the cloud. I don't need to run timemachine as often as it suggests/warns/annoys me about.

How do I disable the notifications? Time Machine is not in the Notifications preferences, and I don't want to stop using it entirely.
When you don't have the external hard drive hooked up, go System Preferences >> Time Machine, and switch it to OFF. You will still be able to perform backups, it just won't happen automatically.

In newer OS versions, you must uncheck the Back up automatically box and then right-click on the backup disk on the right side and select Stop using ‘Time Machine’ Backups.

This is the technique that I use, and I don't see notifications.