Mountain Lion and later OS X releases have a very useful feature where Time Machine can alternate between multiple backup destinations. I use this to back up to both a network share at home and an external drive I keep offsite. Because I only have physical access to the offsite drive occasionally, I don't back up to it often.
After 10 days, OS X gives me a message around the same time each day, such as:
Time Machine is still backing up successfully to the network share every hour, so this message is unnecessary (and the second sentence is incorrect).
I like being able to see when the last backup was completed, so I'd prefer not to remove the disk from Time Machine's destination list entirely. Likewise, turning Time Machine off (as suggested here) isn't an option because I still need my backups to run on the other drives.
Is there any way to disable or delay this message? Ideally I would be able to set it to a longer period of time, so it could remind me to go do an offsite backup every month or so.