You're probably talking about the timeslot that can be shown on the 'reoccuring' section of the Recordings screen. Its not saying it'll record for three hours, instead its saying that it'll record any show with that same name that starts with in that time range.
This is the normal behaviour of the timeslot recordings, and is done to allow a slight variance of the start time of those show (for example, a show running an hour late one week).