Soaking your plants really well a couple times a week encourages deep strong root systems. Why is this good? Shallow root systems are needy and weak. They require more watering and are more susceptible to disease and general abuse. If you do use irrigation, set it up so that it's not running every day if you can. Most gardens really don't need it every day. You'll be glad when you take that mid summer vacation to return to plants that are still alive (because no matter the instructions you give your dog sitters will forget to water).
I generally like to water in the morning, but if you're really busy any time of day is okay unless it's really hot. I like to water in the morning and in the evenings during a heat wave. Drink up.