marree - i cant say ive tried what you describe, but think ive read that 6hrs light /dark does work when flowering cannabis. i would be interested if it does. i guess the weed is still getting the same total amount of darkness, whether or not the two shorter periods would slow down flowering would remain to be seen. what i have read from a reliable source is that you can give longer days to cannabis whilst giving the same 12hr dark period - eg 15/12 and that does allow for more photosynthesis without compromising flowering.