Apple's backup schedule cannot be altered.
I'm not necessarily recommending it, but a utility like Time Machine Editor will allow you to schedule backups whenever you like.
TimeMachineEditor for details.
The interval for the backups is simply altered by editing a single plist file in /System/Library/LaunchDaemons.
You can use a terminal command like this (you would enter your admin password when prompted):
sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 14400
The interval is the "-int 14400" part, and the number is just the time between backups in seconds. The default setting is 3600 or one hour. "14400" would be to do a backup every 4 hours. I use "43200" to get a backup once every twelve hours.
Personally, I always make a backup of the original system file first, before editing the active version. This command will make a copy of that file with the extension *.original.
Bob Timmons wrote:
Unless you are an experienced programmer, the Terminal is a scary place to be.
Sorry, but I don't see it that way at all. UNIX terminal commands do not require any programming knowledge at all. And there's nothing scary about a great many simple terminal commands, provided one does a little reading and self-education beforehand. The op can quite litterally copy and paste what I posted into a terminal window, just altering the number for the time interval they wish, hit return, enter their admin password, and TM schedule is altered the way they want.
Personally, I find installing a system preferance panel or utility app to achieve something as simple and straightforward as this to be the annoying thing - much better to learn a very simple terminal command instead IMO.
Or, honestly, they could just use finder to go to System\Library\LaunchDaemons, open that plist file in a text editor (again, they will need to authorise with admin password), and just change the "3600" entry to whatever they wish - its just a plain text file afterall.
Regardless, this is just a user forum, and a poster can thus do as they wish with the information provided.