is there an optimal time of day that I should be watering?

Marion

I've just been doing alot of reading and research on lawns because I've just sown seed (drought tolerant fescue from LOWE's) and am hoping I can grow an awesome yard in SoCal.

If you have an established lawn it needs to be watered only when it becomes dry, rather than on a regular watering schedule (most people needlessly have a timer set for once a week, or for frequent shallow waterings every few days)

Look for these indicators especially during the hotter, dryer weather:
When you step on it and it doesn't bounce/spring back, or when you see the blades of grass start to curl lengthwise (it's trying to conserve moisture)

When it does come time for you to water, you'd want to do it so that the soil soaks about 6-8 inches. You can push a stick or screwdriver in to test that it goes in easily to that depth.
Also, sandy soils don't hold water well and need to be watered more frequently than clay soil.

Regarding the optimum time to water, early morning is by far the best time because the morning weather generally is cooler and doesnt blow the water everywhere. It allows the water to get to the roots instead of just evaporating. Also, watering in the evening can sometimes increase your chances of lawn disease because the grass doesn't have an opportunity to dry.

I hope this helps.