It's important to kill and remove all of the old lawn and properly prepare a planting area. Install a sprinkler system before the sod is laid, and water the area thoroughly the day before. Try to lay all of the sod in one day.
Seasonal rains begin in Southern California in the fall, so if you are concerned about rationing or want to keep your water bill low, fall is a good time to lay sod. Because the weather will be cooler for several months, the lawn will avoid potentially fatal sunburn. Planting also can be done in spring, but make certain the new lawn gets enough water.
"Sunset" magazine online cautions against laying sod lawns in very cold weather, which is rare in many parts of Southern California, so it might not be a consideration where you live. It also cautions against laying sod during the hottest part of the summer, as a new sod lawn needs lots of water and risks sunburn.