After the plants have reached an appropriate height, you are ready to enter the flowering stage. The height that's appropriate really depends on your growing space. See the flowering stage page for more information about when to switch.
During this growth period, the lights should be kept on 24 hours a day. Your babies need no rest at this time. But they do need water. Make sure that your growing medium is always slightly moist. bianca has also noticed a certain predilection towards hard-core techno during this stage. Wagner and Zepplin also seem to have positive effects. One troll has taken to reading Nitsche and Machiavelli to the plants as well. Research along these lines is very important, and bianca heartily supports such pursuits.