I have a Quick Start RDS deployment on one host under Windows 2012R2, domain member. I applied group policies on this host that limited sessions timeouts:
Windows Components/Remote Desktop Services/Remote Desktop Session Host/Session Time Limits:
End session when time limits are reached Enabled
Set time limit for active but idle Remote Desktop Services sessions Enabled
Idle session limit: 1 hour
Set time limit for disconnected sessions Enabled
End a disconnected session 1 hour
Gpresult shows these settings are applied successfully, and the server drops the sessions according to the settings.