DVRs do not detect whether a program set for recording has begun or ended during the broadcaster's assigned time slot. It starts and finishes recording in accordance with the time slot provided in its guide.
DVRs do have manual software tools that allow users to make adjustments to the selected time slot. Once a timer has been set to record an event, the user can select this timer and edit its parameters. If the ending of an event is the concern, the recording can be extended by as long as the user feels is needed to ensure capturing all of the program. DVRs vary by brand in the precise steps needed to accomplish this task.