Until what time will the tornado watch be in effect?

We interrupt this program to bring you a special weather bulletin. The National Weather Service has issued a tornado watch for the following five counties: Douglas, Johnson, Jefferson, Leavenworth and Franklin. The watch will be in effect until ten o’clock tonight or until cancellation by the Weather Service.
    Remember, a tornado watch means that weather conditions are favorable for the formation of a funnel cloud. A tornado warning means that a funnel cloud has been sighted. As yet, no tornado warnings have been issued for any of the counties in the area.