How tall before 12/12 ?

I'd like to know when some one brings you bb's all reddy rooted n such , they should be around 7 days? and if so do you count life since day 1 of the cut ?
And also would like to know when is the best time/height to 12/12 (on a productive and tight schedule) .

i leave mine for 3 weeks on 18-6 then put them on 12-12 on boost

It depends how big you want your plants to be.

yes i once left em for 5 weeks on 18-6 ,they was massive ,but did get a good yield ,also depends on what space you have in your room ,