Sometime between 9:30 AM and sunset. Can't be any more specific than that. I usually mow on the weekend, so to allow my neighbors a chance to sleep in in peace, I wait until 9:30 or 10:00 to fire up the mower. If I water in the morning I wait until late afternoon to allow the grass time to dry out before I cut it. Then there are days like yesterday when I decided to do the yard after work so I won't have to do it this weekend and can spend time with my 9 year old neice who is visiting until Monday.