hey hydro65,
the watering frequency of an Ebb & Flow system generally is determined by the media being used.
Hydroton or
grow rocks do not hold water so it will have to be watered often, once an hour, minimum.
soil-less media, peat or coco can hold much more water than hydroton so watering less often is OK, once every 2-3 hours
Rockwool holds a lot of water so it will need less watering per day then the others, once every 3-5 hours
the watering duration should be just long enough to wet the media.