The best time to water will depend on several things such as is the lawn brand new or established? If you have your watering system set to a timer, you can easily select when you will water.
For established lawns the best time to water is in the earl morning, just before sunrise. This allows water to fully soak in. In the cooler morning evaporation is at a minimum so you are more efficiently using your water. Wind is usually calm minimizing wind drift and allowing sprinklers to maximize coverage.
Evening water should be avoided. Evening watering keeps the ground moist for long periods which encourages a number of diseases that will weaken the root system of your lawn.
For newly installed sod lawns, you need to keep the freshly laid sod from drying out. Set your system to come on 4 times a day and water enough to keep the sod moist at all times. Continue this until the roots have a chance to grow into deeper soil.
For new lawn, always use the highest quality, fresh cut sod available from your local Vancouver, WA sod farm, Far West Turf and Nursery.