Can I have time machine backups on different schedules?

I have Time Machine backups set up to a network drive and to an external hard disk. They are currently set to back up hourly.

The backup to the network drive works fine. But the external hard drive is usually in my desk. I only plug it in a couple of times a week. Because of this, every time I open up my Mac, I get a warning that the Time Machine backup hasn't happened.

Is it possible to keep the network drive on the hourly schedule, but put the external hard drive on a manual schedule (only back up when requested)? I can't find a way to do this.