Hello dropkick, Technically it’s 3hrs and 59min which is just a min shy of 4hrs. I’m sorry but there is no way to increase it more than that. You could however use multiple start times. Each program has up to 4, which would give you about 16hrs of watering. If you wanted any more than that you would need to use multiple programs. Also just so you know there would be a delay of a few seconds between each runtime, station, and program. Please let us know if we can help out with anything else!