Hi, got a strange problem. At the start of the month I added 2 manual timers to record BBC Radio 2
One records from 12 am - 12.01 pm
Another records from 12 pm - 12.01 am
The timers are set to record every day of the year.

Most of the time the recordings have been the correct length as they should. However 6 times in the past month I've had recordings that have been either:
10 hours 50 mins or 13 hours 10 mins long.

Why does this happen? Any idea how I can fix it? Thanks