Wait to transplant them out of the small nursery pots until they have 2-3 sets of adult leaves. By that time, they are probably getting close to rootbound, and you want to time transplants by the condition of the roots.

Bob may have been busy with other sections of the boards, or didn't feel that this was his particular area of expertise- I think for some reason that he knows hydro better? Not sure. Anyway don't worry, that's why we are all here, to pool our collective knowledge!