alsfan, believe me when I say that I am not 'ducking the question' but it depends on the area, the type of ground, the amount of water you want to put on and the crop.
Measure and calculate the area in sq.ft. Ascertain how many gallons of water will be needed to provide 1/2" of irrigation (a working standard) to this area. Divide this by the total gpm of all the sprinklers which cover this area. This will tell you how many minutes the zone should be run. Now for the fun part!
Some plants require very different watering programs. eg. a cactus patch vs. a grass lawn.
Some soils cannot accept or hold much water (eg. a heavy clay) and will quickly cause runoff (a total waste of water, time and money) which must be avoided.
It sounds complicated but it is not difficult. The real benefit is the inner satisfaction that you are doing your small bit to effectively manage earth's scarcest resource-the one which may well turn out to be the limiting factor of life on the planet.

Check with your local water department. Ours has a free service where a rep will come out to your house and help you determin it. He was here three hours for my 16 zones. Best part - it was free service.