While there are no set parameters for this, here are a few rules of thumb. The precipitation rates on gear drive/sprayed zones are about a 4 to 1 ratio. This means that gear drive zones should be run @ four times longer than spray zones. Gear drive zones should be run for a minimum of 30 minutes, except in very shady areas. In the hot parts of the summer, these should be changed to 45 minutes, even an hour. Sprayhead zones should be run for 8 to 10 minutes, and bumped up to 15 to 20 minutes in dramatically hot weather. In the spring and fall, you should be able to get by with every second or third day. When the weather gets very hot, once a day is a good idea, as this will keep the lawn from getting stressed. Time and experience will tell you what will work best on your own property.