The best time to water your lawn for optimal lawn health and great results is in the early morning hours such as before you go to work.
When watering your lawn it's best to water the lawn between the hours of 4:00 AM to 10:00 AM before the sun gets too hot.
Watering your lawn when it's hot out and the sun is beating down will evaporate the water from your lawn and could lead to burning the lawn as well.
So before the sun gets too hot it's best to water your lawn then so water the lawn if possible in the morning before work or when you wake up if possible.
If you can install timers to start the sprinklers at 4:00 AM and water for around an hour which is usually long enough.
Also watering the lawn at night is bad for the lawn as well so if you can't water on a weekday do the watering at least twice per week in the mornings on the weekends such as when you're not going to work.