The Desert Botanical Garden in Phoenix gives this advice (I'm thinking from the standpoint of someone who lives in desert) and of course drip is the normal watering method here.
"DRIP IRRIGATION: If you are using a drip irrigation system, be sure that the system runs at least two hours for each watering. This will ensure that the plant is being watered deeply. About every fifth watering, let the drip run for 8-10 hours.This will leach away any salts that have accumulated around the plant."
So I think 8 -10 hours would be reasonable limit. We have high alkaline soil, so if we don't get watering that goes beyond root zone, then there is salt buildup which will kill plant.
Out side the scope of this post, another nice feature would be something around alkaline soil, which would automatically do a long cycle and flush salts periodically. Lots of places have this kind of soil