I finally got some time to play with this today. The timer is working. After playing with the code I managed to get the numbers to display all the time. The reason they were not is that the program did not display anything while waiting for the timer flag to be set.
Two small problems I hope to fix shortly. One is that each time the display increments, it goes blank for maybe 100ms. I've tried several things to fix this but they only make the blank period longer or slightly shorter.
The second thing to fix is the pulse count. I need to count 72000 pulses before incrementing the display. Problem is, timer0 is 8bit and limited to 256 pulses before rolling over. I need to have timer0 rolloever and each time the flag is set, but it into a register and increment it until there is the equivilant of 72000 pulses.
If I preload the counter with 5, and have it rollover after 250 pulses, and do this 288 times, I get 72000 pulses which equals 1/10th of an hour. Would that work?