Most strains are pretty consistent in the same environment. If your AK47 took 9 weeks (from when u first see flowers) it will generally take about the same every time if u dont change anything. This is not true of the TIME it takes for them to begin flowering, as hydrogreen has said there are many other factorss (size of plant, training, lighting, ect) that will make a plant begin flowering faster or slower, so measuring from when u go 12/12 is really not very effective.