Custom Scheduling of Time Machine backups
Schedule backup for every 4 hours ( 4*60*60 = 14400 )

sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 14400


Default is 1 hour ( Rollback procedure )

sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 3600


Source: http://osxdaily.com/2012/02/02/change-the-time-machine-backup-schedule/