You still have not explained yourself well. Are you planning on putting the clone into 12/12 to root and then put it back into 24/7 to veg and then putting it back into 12/12 to flower?
If you are dealing with clones, you can put them into 12/12 whenever you want--they are sexually mature. However without some kind of vegging phase, the plants will be very small and (yes) produce only a couple of grams of bud. You can leave the plant in vegging for as long a time or a short a time as you would like, depending on how big you want the finished plant to be. Once you put the plant into 12/12 it will only grow so much taller (different strains vary).