I’ve tried really hard, not only with the settings provided by khedron but also playing with xscreensaver, xset and light-locker settings.
In my understanding, gnome settings daemon overrides all those settings (I think that about every minute) and makes it impossible to make them permanent. For example, if you set ‘xset s 60’, the screen will go blank in a minute and will trigger light-locker, but once resumed from idle, ‘xset -q’ returns different values (everything is set to 0, both screensaver and dpms). If you choose values that are something like ‘xset s 240’, the screensaver will not be activated after four minutes because those settings were overridden.
I really have no idea how to stop this behaviour but I hope it can be of any help. The only way I have managed to dim and turn off screen when desired in my laptop is by using dimdaemon from AUR.