My alarm clock is fifteen minutes fast. My wall and computer clocks are set to the correct time. My car clock is two mintutes fast. There are, to me, good reasons for each. I don't think I need to explain why my clock, computer, and other incidental clocks are set to the right time. I look at them when I want to know what time it is.
The other timepieces are part of a plot I've hatched to trick myself into not being late. The alarm clock is fifteen minutes fast because the subtraction of fifteen minutes is easy throughout the day when I want to know what time it is, yet difficult when I'm half-asleep. That helps to get me up on time.
My watch is five minutes fast because I'm a visual person. The watch is an analog watch, so I see time represented as actual segments of space on the watch face. When I look at the watch, even though my mind knows the true time is five minutes earlier, the visual impression of the time presented on the face is strong enough to leave me feeling I should hurry.
My car clock, too, is in on the conspiracy. It is ahead a mere two minutes, an interval so small that I usually forget about it and assume the clock is displaying the actual time. That way, I'm two minutes less late than I would otherwise be.
While my mind knows, of course, that these timepieces are fast, the deception still works on another level. I'm still not terribly good at being on time, but these tricks keep my tardiness to about five minutes on average.