shawn47 - the best time, in my opinion, is just after sunrise on a day that's not likely to be cloudy. This gives any water that has splashed on the leaves time to dry out during the day.
To tell if your plants need water, stick in you finger around the root zone, if it feels moist, or even vaguely moist, no water is needed. I water about every seven to ten days when the weather is hot.
The worst time to water is late in the day. This encourages fungus.
Water at the root zone ONLY. Try to avoid splashing water on the leaves.
After a heavy rain shower, put about a two inch layer of mulch around your plants, this will help retain moisture in the soil.
I water in the early evening/late afternoon. Mainly because thats when I have time, but like Sweetie77 says, this allows for the ground to hold the water longer without evaporation.
On the weekends, I water part of the garden in the morning and another part in the evening. I do this so I don't over-draw my well in dry weather.
I, too, water in the evenings, usually right before sundown, cause that's when I can stand to be out in the heat. I water close to the soil, close to the root zone, and don't splash water up on the leaves, to discourage fungus growth, as HoneybeeNC said above.
Weekends, I water early and late.
I just love the yard after everything's watered in and standing at attention, saluting the Son!
since it been geting up to 100+ every day iv noticed the soil in my pots on the balcony is dry when i get home at about 6 PM. so iv been watering them 2 times a day.in the mornings and evenings. so far they seem to be remaining perky except the spinach which i think just cant take the heat.