the only assumption i can make is that he is talking about how long he has to wait until the fish and bacteria have fully developed for him to be able to start growing some plants, and my best guess is about a month or so, that way you can make sure that the fish are going to survive and that the algae/bacteria has established itself, but what you have to understand is that the entire system is an ecosystem with each part playing its role. you may want to start the plants earlier than this because it will aid in making the other two parts better.