We should not start watering the lawn until the freezing nights are over. For most of the Wasatch Front, this will be sometime around the middle of May. If you turn on your sprinklers before the last average frost date, you will risk freezing and damaging your irrigation system.
Also, the frequency and duration of your lawn watering system should be set to only once or twice a week for May and June. As the temperatures go up, you can increase your watering to 2 or 3 times a week, depending on the weather.