If not already configured, ensure that users cannot change GNOME3 screensaver lock settings
by adding /org/gnome/desktop/screensaver/lock-delay
to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification.
For example:
/org/gnome/desktop/screensaver/lock-delay
After the settings have been set, run dconf update.