If its losing time on every change of the hour, and the total loss is 2 seconds per day, then each change of the hour would lose 1/12th or 0.083 seconds.

@ 4mhz, that's 83,000 instruction cycles. No, I don't think it's accidently losing that many instructions to increment an hour. And, looking at the ClockCount interrupt routine, if that were the case, it would also happen on every second, minute, and day as well. Which it doesn't.

Why don't you think it's the crystal?

Have you measured the frequency?

DT