Contrary to many beleifs, you should always wait for plant to mature. Which is 3-4 weeks in.
From Book Below
" Always wait to induce flowering until after the pre flowers appear. Inducing flowering before pre flowers develope will stress plant. This stress could cause odd growth, and might cause Hermie.
Induceing flowering before pre flowers show does not speed up flowering.
Flowering will occur at the same time as if you waited for pre flowers to show."
I shortened it a bit but thats from The BOOK.
True true, alternating nodes.For future reference you should have at least six nodes and to make sure it is mature they should be alternating before you put it in flower. I don't believe in 12/12 from the start but I'm not going to start a thread of arguing about it, I know that is how a lot of people do it and claim it's the best. I like to grow a nice size mature plant before going into flower, but that's just me.