I usually water in the afternoon around 5pm since I like to see my sprinklers working, and I have 6 zones, each 15 minutes each. I water 15 minutes each during spring and mild summer, and when the weather gets hotter, I pump it up to 20 minutes each. (But that's just me)
My yard is in the sun from 7am till about 5pm. I've always watered in the afternoon so it can soak in. Not once have I ever had a problem with mold, disease, etc.
The grass always has dew forming on it when it gets dark whether I water or not, and it dries out all mid day in the sun. End of day, I give it a good soaking.
I'm no expert..........YET!
I just like to suggest things and learn...
See what the pro's have to say first.