Make Gnome screen lock after 1 hour, not 15 minutes?

You can put the desired values directly in GSettings, either via the dconf-editor app (i.e. "GNOME regedit") or command line:

• Timeout for blanking the screen (seconds; 0 = never):

  gsettings set org.gnome.desktop.session idle-delay 3600
  

• Timeout for locking the screen after blanking (seconds; 0 = instant):

  gsettings set org.gnome.desktop.screensaver lock-delay 0
  

This can also be accessed by using:

• Settings -> Privacy