you dont get much from 12/12 but some are in a hurry for any an this is quick an aesy fer new grower, bttr off if ya can to get a bit of height in the veg cycle much bttr yields, I alwys veg for at least 6 weekssometimes 9 witv serious abuse (topping last supercropping lollipopping etc but dont worry bout that yet).
the length of time for flowering is determined by the plants genetics and is accurate ime in optimal grow enviro so fer most hybrids eg ww (got one in mid stretch at mo beautiful plant) take between 8-12 weeks depending on indica/sativa balance and a few ovva thing.