Hey, it takes about 1.5 - 2 weeks before the plants will adapt to 12/12 after this initial period the plants will start to produce flower/bud @ the bud sites usually at the joins of the branches to the stem. The buds will slowly start to grow but they wont fill out untill the last 4 or 5 weeks of flowering then you should see a speeded up growth. I suggest you find out how long to flower you particular strain so you can pick them when there at there peak thc levels. Anyways, hope this helps.

Peace