How to change GDM login screen blank delay

Hello,

This request is for Ubuntu 18.04.2 LTS using the default GNOME display manager.

When the systems boots or gdm/gdm3 service is restarted it takes 5 minutes for the login screen to go from waiting to blanking and powering off the screen. This is a great default blank delay for login.

However, any subsequent interaction with the GDM login screen results in it blaking after 15 seconds which for my purposes is way to short.

With some fairly extensive googling I've been led to search for and set various dconf and gsettings, but nothing seems to actually change the behavior at the GDM login screen.

Also in some cases it seems like it blanks even faster like 3-5 secs. But I have not figured out what exactly circumstances replicates that yet.

Please let me know how I can increase this subsequent timeout period until the screen blanks and turns off.

Thanks!