switch it off manually when you want it off either at plug or via the router set up screen
you should have been able to set the times to switch off wireless on that router if it did go wrong its most probably time for a new one
i think it is capable of blocking devices by mac address to if its working via the The Access Restrictions Tab
there you should be able to see the pc tv etc and pick times they can access the router
but other than the first method and or disconecting the network cable going to the device ALL can be got arround by a determined user if left alone
nothing works as well as doing it manualy