TimeMachineEditor allows you to change the times that TimeMachine backs your system up. You can change it to once a day, week, or month; and control the times it backs up at. On the developers website, they mention that this program doesn't run in place of TimeMachine, rather, it just changes the interval that the system backs up. TimeMachineEditor is available as freeware from the developer's website or from MacUpdate.

As a word of caution, use this at your own risk, as the developer doesn't provide a way to reset the original settings of Time Machine. They also mention that the "Latest backup" time may be incorrect in the Time Machine System Preference pane.