Just before sun rise

When its not windy, and not during the heat of the day, and not when you want the water pressure in the shower!

Most of the time, the hours between 4 am and 6 am is when I try to water residential. Some comercial systems water for 12 hours. If you want to water at 10 PM, thats fine, some folks say that their is more risk of lawn diseases if the grass is wet all night, but I don't think these people have lived in a humid climate. Our grass here is wet everymorning regardless of watering.