Time machine

For ages the clock in my car has been eight minutes fast. I quite liked this as it seemed to me that I always arrived earlier than I thought. However, this week I decided this was silly and so I set it to the exact time. Snag is that I still seem to arrive at the same time that the clock says, making me late.. Most confusing.

It is as if the car clock is some kind of absolute time which can't be changed. I'm going to set it to an hour fast and see if I arrive at work before I left home.