Smokey is so very correct my friend. 12/12 from seed or not as an example will not flower until the plant is sexually mature. We just speed up the process when we force our plants to flower.
He only asked how early "CAN" you flower a plant, which means he most likely wants it done as soon as possible.
i am only stating that it can be done at almost any given time.
However, smokey says 3-4 weeks, which is incorrect because it can be done earlier. (all though not really recommended)