I want to know whether it's possible to set-up a schedule to turn on/off the radio/WIFI transmission for the Airport TimeCapsule?
The Timed Access controls will allow you to set up a specific timeframe each day when wireless devices are allowed to connect to the network. So, the rule that you would set up would look like
Everyday........Between.......7:00 AM and 11:00 PM......or, it might read 23:00 if you are using a 24 hour clock
But, the wireless will still be "on" at all times......since devices can only connect between 7:00 AM and 11:00 PM, devices will not be able to connect between the hours of 11:01 PM (23:00) and 6:59 AM.
So, if your question is really asking can the actual wireless transmission be turned on and off at specifiied times, the answer would be "no".