The fire timer can become messed up if you've repeatedly paused the game using the space bar and then changed game speeds. It can also grow very large if your computer's system clock has been adjusted or is unstable. Depending upon the cause, you may be able to restore the timer to normal by having one of your villagers put wood on the fire (to recalculate the timer). If that does not resolve the problem, let me know and I can give you a more complicated procedure to reset the fire timer to normal.