Don't rely on your time-clock to set up an irrigation schedule. Instead water only when your lawngrass turns a wilted gray-green color. It is important to water deeply applying 1/2 to 3/4 inch of water to wet the entire root zone. If you do not apply enough water a shallow root system that is even more sensitive to drought will be the result. To determine how long you should water place several cans or rain gauges out in the sprinkler pattern to catch water until the desired amount is applied. It is very important to avoid frequent light irrigations that provide a perfect environment for diseases and stimulate excess growth that leads to thatch problems. If  you are leaving your property for a long period it is generally safe to set the time-clock to run about every 5 or 6 days, your water output test will let you know how long each zone should be.