There is your answer... You want the rockwool to almost dry between feedings. How people drip and are successful is a mystery to me. A waterlogged hugo is not a great environment to grow in.a big plant in bloom can take about a gallon a day maybe 2 a small plant it could last for a week, it depends on your environment there.
You can soak it till there is run off. Just let it dry out a bit before the next watering. It should be easy enough since you are hand watering.So it's accurate to say about 2 cups, 500ML per plant per day?