@lford The one minute difference could just be a slight rounding display since we only show minutes and not seconds. It could be a few seconds difference.
Exposure might slightly affect duration, but largely affects the watering intervals since we use exposure as an offset of crop coefficient. (less exposure pulls down the crop coefficient, which pulls down your daily ET...i.e. the plant is transpiring less per day, so needs to water less frequently)
For a test, I created one zone with lots of sun and it is going to run for 37 minutes, every 8 days. I also created a mostly shade zone that runs for 37 minutes and waters every 5 days.
Hope this helps.