each grow has it's own characteristics. However, generally you ebb for 15 minutes 2wice a day. vermiculite tends to keep the rootball a little too wet.

V is used for cloning,propagation...etc.
if you were using rockwool then You might only water once, but that would depend on whether or not you are using slabs or blocks backfilled with hydroton or rocks...etc.

With the method you described...2 times a day should be plenty...the point is to allow the roots to get oxygen...thus the need for you to have your medium on the drier side before ebbing again. hope this answers your question and gives you some insight on the subject.