Apple - How can I set Time machine interval to several minutes in Mojave?

NVM I figured it out.

This is a great timing to finish the answer, right? ...No? Okay I'll show you what was the problem then...

What is required to do that in Mojave is:

1. disable csrutil.
2. sudo vi /System/Library/LaunchDaemons/com.apple.backupd-helper.plist, and then edit Interval, Delay, GracePeriod. I just set them to 1/4 of original value.
3. Reboot. You were going to re-enable csrutil anyway, right?

After that, time machine prefpane will still say it's going to backup 1hr after last backup, but automatic backup happens 15 mins later in my case.

Try the free utility TimeMachineEditor. It allows you to set just about any kind of schedule you want. Way easier and way more versatile than manually editing files.