tms8c8:
That's what I was asking: is there a way to keep track of time through some sneaky manipulations or using the watchdog timer somehow. Evidently there is not.
You can, up to a point. You could have Timer1 (the 16 bit timer) used as a timer. With suitable prescaling and counting modes set up, it could time quite a long period (eg. 8 seconds). There is a trade-off between resolution and the time before it wraps around.
But, I just don't like the idea. 
The time for an interrupt to start executing isn't exact, so your adjustment won't be precise. You are better off keeping interrupt handlers short (well under a millisecond) and doing what you want by keeping track of elapsed time.