UPDATE: After observing this for a day or two, I can see that the idleTime is set to 5 minutes within System Preferences while
defaults -currentHost read com.apple.screensaver idleTime still returns
The options to change the delay time within System Preferences is grayed out so I couldn't change it.
So I tried setting it with
defaults -currentHost write com.apple.screensaver idleTime -int 300
After running that command, I'll get this.
$ defaults -currentHost read com.apple.screensaver idleTime 300
However, once I go back to the screen saver settings in System Preferences, the delay goes back to 20 minutes and I get this.
$ defaults -currentHost read com.apple.screensaver idleTime 1200
The global default is set to 300.
$ defaults read com.apple.screensaver idleTime 300
I've also tried deleting the whole
com.apple.screensaver domain and then go back to screen saver section in System Preferences, and I see 20 minutes and 1200 again.
I have a profiles in place where the screen saver idleTime is set to 300 but I have no idea why it's getting set to 1200.
This is on Mojave 10.14.1 (18B75).