Every property is different, even if the sq. ft. is the same. I don't see how a formula could be made. A football field won't take as long to mow as a roadway will that's full of holes, bottles, sand drifts that change weekly, etc. If the sq. ft. is the same, other things can slow you down which will make the formula useless. This is the way I see it anyway. Either way, it's a good question.
8 years in the business.
Oklahoma Licensed Pesticide Applicator (3a)
2012 Hustler X-One 60", 26hp, Flex Forks, Mulch Kit