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:


disable csrutil.
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.
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.