I actually did not have my system up and running until my seedlings were about a week old. At first I just had them in the cubes on a plate and wet them evertime they got fairly dry. If you have them in the system, you should not have to hand-water them because the water pump should do that for you via the feeder tubes. If you do not have the feeder tubes then I would say wait until the top of the cube is almost dry but still a little damp, then water. Another option if you don't have the feeder tubes is to raise the water level in the reservoir about 1/2 inch up the net pot and gradually lower it as the roots grow.