Time Machine is the built-in backup tool of Mac OS X and if you have enabled it on your Mac (See: how to setup Time Machine) then it refreshes backup after every 1 hour. As Time Machine on Mac is set to take backup after 3600 seconds which represents to 1 hour so whenever you have to change time machine schedule you have to provide the value in seconds according to your desire.
Although, there is no max. or min. time limit is described to set as Time Machine backup interval but just for the sake to save system resources do not change Time Machine backup frequency too much lower for example, a few minutes.
Follow the steps given below to change Time Machine settings.
Click on “Finder”
Navigate to Applications > Utilities and launch “Terminal”
Suppose you want to change time machine backup frequency to 3 hours, then use the equivalent value of time in seconds as 3 hour = 10800 seconds.
So, type following command in Terminal and press Enter
sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 10800
where int 10800 = time in seconds equivalent to 3 hours
It will ask for password so enter your Mac password and press Enter and that’s all.
Now, time machine backup frequency is set to every three hours on your Mac.