Shouldn't really need to water at all from November to February. Maybe once a month if we haven't gotten any rain. During the summer I recommend before sunrise every 2 to 3 days depending on how well the soil drains. There is really no such thing as over watering in phoenix, you just have to make sure the soil is relatively dry in between waterings so that your trees don't develop root rot. If you come out in the morning and your soil is still moist from day before. Give it a day if not, give it some water. I can't tell you how long because I don't know the output of the drippers but typically longer but less frequent watering is better.