@scottsh,
Normalizing on inches (or millimeters) of water makes a lot more sense to me than using uncalibrated time units for irrigation.
The not-to-exceed watering time to prevent runoff is a great idea.
Defining zones as overhead irrigation such as lawn sprinklers (rated in inches per hour) vs drip tape (rated in gallons per hour) for crop and vegetable irrigation would be a useful addition.
Long term for your next plug-in 🙂 , Fertigation valves in series with the irrigation valves that know the crop type and nutrient requirements over the growth cycle of the plant once the planting date has been specified would be awesome.