10,000 gal @ 80 gpm will give you roughly 2hrs of run time before your out. That is assuming the tank was full when the cycle started.
I say "assuming" because if you are using a mechanical float valve you will sometimes catch it in a low position where is is about to kick on the auto fill. A lot of people do not factor that in and run the tank dry. A foot or two difference in a 10,000 gal tank can mean a 2,000 gal holding difference.