That's about as fast growth as you can expect. I notice the difference every day. It kind of sucks that some stretched so much at the beginning. You might have to end up using toothpicks and twistie ties to hold them up because the leaves will get big and heavy soon. You do have a nice breeze blowing on them, right?
When you say "break their shell," are you germing new seeds? If so, you want the tap root to be about 2 mm long and then as soon as you plant it in the soil put the light on.