Three rows, of time coordinates, are generated when after adding start and stop times for a thread schedule.
This behavior is by design.
Thread schedules are based off of a 24 hour time cycle. When created, the time before and after the schedule is included to graphically display when it will be active, and when it will be inactive.
A screen shot showing a thread schedule is attached. It is active from 08:00 to 09:00 and illustrates how the schedule will be used..
Describe resolution here