A good guide is to irrigate to the point when the water starts to run off OR you have got 1/2 inch of irrigation, whichever occurs first. You can determine the inches part by setting out some straight-sided cans or jars, running the system for 30 minutes and measuring the height of water in the jars with a ruler. The reading expresses, as inches of rain, how much irrigation has occured. If there is a significant difference in any of the containers, this would point up a "dry/wet" spot or malfunctioning head.
When the system is running, it should look like a light rain.

Lot depends on what your watering and what type of heads and nozzles you have running. Spray heads put out more water than rotors. I think the general consensus for most grass is 1" of water a week.

please dont put cans on your lawn. that is just stupid. water your lawn 2-3 times a week heavy. this causes the grass to stay green but on the off days also causes the grass to "starve" for water which has now drained deep under the roots of your grass. thus the roots will grow deeper to find the water making a strong and healthy lawn. for rotating heads, go 1-2 hours 2-3 times a week. for misting heads go 30 min - 1 hour 2-3 times a week. the sandier the soil, the more frequent you will need to water. good luck.