It is difficult to give a precise answer, as every drip system will be treated differently. There are many factors that will affect the run time such as flow rate, soil type, plant type, spacing, and environmental conditions. Below is a basic formula to determine how long you system should run in a hot and dry environment.
(Canopy Diameter x Canopy Diameter) x .01 = Plant Gallonage Requirement
Ex. Tree with a 15' Canopy (15 x 15) x .01 = 22.5 gallons per day
Ex. Shrub with a 3' Canopy (3 x 3) x .01 = .9 gallons per day
Note: the above equation is for hot and dry environments, the water requirement will decrease during cooler conditions.