This handy PDF will help you determine the length of time needed to provide one-inch of water to your lawn per week. Depending on your local weather conditions more or less water may be required. These recommendations  are based upon no other source of water received during the week (rain, sprinkler watering, etc.).
Recommended Sprinkler Durations [PDF -68KB]
Based upon the rule of thumb of providing one inch of water to your lawn per week; total water delivery (rain + watering); warmer, more arid areas require more.
These rates are based upon no other source of water received during the week.
Recommendation based upon sprinkler coverage area: divide your watering area by sprinkler coverage and multiply that ratio to the recommended time.
Flow rate and coverage area assumes water pressure from spigot is ~ 40 psi