If you must water your lawn, the best time to do it is in the morning. That's when the temperature is the coolest and the water has a chance to soak the ground and then evaporate off the blades of grass as the sun rises. But don't think watering the lawn at night is just as good. While water may have a chance to absorb into the soil, the wet and dark conditions can actually create damage or disease to your lawn.
ANDREWS MCMEEL SYNDICATION