Flowering Question

I have a seedling with exactly two true individual leaves. It's a mostly sativa strain. I know some people start flowering at about 12 inches of height. I know mine's gonna be leggy and might not want to wait that long. I want roughly one oz cured.

Like I said, it seems that many judge this on height but I'm looking for a number of leave sets or fan leaves. I don't want to rush it, but I also don't want to be fighting the height of a leggy plant in 6 weeks.

Figure an average top drip rockwool hydro, 2x4x5 area, with 400W hps.

Thanks.
 
Top