Digital clocks that I am familiar with are controlled by an integrated circuit known as a "clock chip". Perhaps yours is defective. As to the location of the chip, you are on your own. I have no knowledge of the circuitry in the 986. My best guess would be in the instrument cluster, but you never know with technology today, it could be part of the main ECU. If you could find a used instrument cluster to try out, it may solve the problem. If it were me, I would just get good at resetting the time every couple of weeks, cheaper fix and less work than trying to find the problem.
The astronauts have proven that the faster you go, time slows down. Maybe you are driving too fast.
