Scheduled record time is off

I've noticed a problem with my DVR record timer for awhile.  It seems to start the recordings a minute or two ahead of schedule and runs over time from about 1 to 3 minutes.  At least it isn't clipping any programs short, but it's annoying to have to fast forward through the first 1-3 minutes of a recording because the previously recorded show (if recorded back to back) is at the beginning.  Is there any way to get the DVR's internal clock back in sync with the real-time program schedules?