you might be a little confused, your drip system shouldn't be on the seedlings at this stage before they get roots through the cubes. The only way you could do this would be to have a super slow drip, but most saturate the rockwool too quickly and will stunt your growth. Rockwool is made to wick up moisture almost as a reserve to where the roots are from the bottom up. Always water at the bottom, and dont plant until the roots are showing adequately out the sides. Seedlings and clones are not ready to be put in hydroton or soil until the roots are showing. It is better to underwater at this stage than to push it with the drip system, only because rockwool has amazing water retention abilities. When they are light weight they need to be watered. Judge by weight rather than by eye.