1. do you think response to 12/12fs is strain dependent? Do some perform better than others?
I think some strains do perform better than others (dels' bubblebomb conconction, for instance), but for me, sativa-dom plants are very well suited to it, and don't lose much in yield.
2. I grow NL and for me it flowers 8 weeks, 9 tops. Does that mean my NL would harvest in 9 weeks from seed?
I'd say you have to add a few weeks to that number, as they don't flower immediately, but go through a veg stage, even in 12/12.
3. what might I sacrifice in yield?
With satvia-doms, I'd say not that much (and I really think my 12/12 fs OJ haze will yield the same as the ones I vegged for 4 weeks.
4. if it doesn't in 9 weeks, why not just veg 24 hr for a week or 2 before 12/12? It does seem like 12/12fs might really be vegging for x time, but vegging at 12/12. I don't see the advantage in that except, as with me, you want to start seeds in the same room where others are going 12/12.
They definitely are vegging for a few weeks, even in 12/12. Personally, I don't like having lights on for 18 hours a day, and really, if they're vegging in 12/12, then why go to 24 hours? For a more robust veg? Hmmmm, not sure that 24 hour veg is more robust than 12/12 vegf.