Isso funcionou para mim:
Start/Search and type gpedit.msc, Right click the gpedit results and
Run As Administrator. In the Elevated Group Policy Editor, on the Left
Panel, go to User Configuration/Administrative Templates/Control
Panel/Personalization/Enable Screen Saver and enable the Policy.
Once you have enabled that policy, go down and also enable Screen
Saver Timeout. Note that in the Screen Saver Timeout policy there's
an option to set the number of second for the timeout with the default
being 900 seconds or 15 minutes.
Once you've enabled both policies and set the timeout if different
from the default, exit the group policy editor. If you now go the
screen saver settings in Control Panel you will notice that the wait
period will match the minutes you entered in the group policy editor
but it will be grayed out preventing you from changing the value
unless you go back into the group policy editor and change it there.