Kill inactive user sessions on a Windows Server 2012 R2 Terminal server

Edit:

Gah...I'm sorry, I didn't check your question correctly...Terminal Services are Remote Desktop Services now since Windows Server 2008 R2 (I think). Sorry!

Check your RDS settings on the server itself - not GPO -, under

Remote Desktop Session Host Configuration

(override user settings) and try specifying the time limits there.

Check the following GPO settings:

> Computer Configuration\Policies\Administrative Templates\Windows > Components\Terminal Services\Terminal Server\Session Time Limits

Your GPO settings are only for RDP sessions, not for Terminal Server sessions.