Courtesy of 9 News, this is the current temperature at 8:30 PM, on this day of July 18, 2011. 86 degrees! Imagine how much evaporation is still occurring vs the estimated low of 64 tonight, which will be at about 5:45 AM, not to mention it will be a full 22 degrees cooler!
So, do everyone a favor a switch your watering time to the morning right before sunrise. You will even be able to use less water as more of it will be absorbed into the turf!