You can use CDR Analysis and Reporting (CAR). Go to CCM Admin -> Application -> Cisco Callmanager Serviceability. Click Tools -> CDR Analysis and Reporting. Click CDR -> Search -> By User/Extension. You can then search for a particular extension and time range. You'll then need to click View to get the start and end time for the call. There are other reports that will give you this info as well. If you've never used/setup CAR, see the link below regarding installing CAR and configuring the necessary service parameters.
