Registry tweak to unlock GUI for the Lock Screen display off timeout.
When your PC is locked, the normal display off timeout value has no effect on it and you cannot specify the timeout value after which the screen will turn off while you are on the Lock screen. Turns out, there is a hidden registry setting for this and enabling it even turns it on in the Power Options control panel GUI - the same window where you specify other power related timeout.
This works in Windows 10, Windows 8 and Windows 8.1