I have a small closet set-up with a fan, 1 halo bulb and 3 CFLs and one of my plants is nearing sexual maturity (3ft, alternating nodes) and i want to change it to a 12/12 schedule, however I have 10 other plants in there at younger stages (8 seedlings and two 1' ones). I am wondering if these younger plants will grow on the 12/12---I'm mostly worried about the 1' ones since one has recently shown pre-female parts (they are all currently on 24/7). (I have been trying to figure out a way to subdivide the closet into two separate light cycles, but nothing has seemed feasible.)
I grow all my plants in the same cab on a 12/12 cycle. Younger plants still grow, not as fast as they would on 18/6 or 24/0, but they still grow fine. They do not get very large (for me at least) because they flower as soon as possible. Your 1 footers will probably begin flowering along with the large one, since they have shown pistils already.