Check Soil Moisture to Determine Watering Time
Common wisdom for establishing the correct length of time to water is to place a pie pan in the yard and note how long it takes to fill 1/2 in. deep. But experts prefer a more accurate method that takes soil conditions into account. Heavier soil doesn't absorb moisture nearly as fast as loose or sandy soil, so it needs to be watered longer.
After an extended warm, dry period (dry soil is the key) set up your sprinkler and set a timer for 30 minutes. Then turn off the water and check the soil for moisture depth. Do this by pushing a shovel into the lawn and tipping it forward to expose the soil. See how deep the water has penetrated. Moist soil will be darker. Your goal is to run the sprinkler until the water penetrates 3 to 4 in. into the soil.
If the water has not penetrated far enough, restart the watering and continue to keep track of the time. Check again in another 15 minutes. With trial and error, you'll eventually arrive at the optimal length of time to water for your soil type and water pressure.