Do you mean the reload is too long and makes the timer ISR too long? Nooo, if you need more than 8-bit reload (with 8bit the autoreload is available for timer0 and 1, too), the reload itself takes hardly too long, especially if it is of the "mov th,#const" type...

Or do you mean the body of timer ISR? Oh than that's too bad anyway and needs to be redesigned from start.

Or any other ISR? Then that's why priorities are around; the timer routine needs to be of highest priority.

Jan Waclawek