I know where you're coming from, but this game we play is one of patience. Rushing things will most certainly NOT give you maximum yield. Maximum yield comes from good genetics + optimum environment + optimum lighting x patience. If you begin your 12/12 phase when the plant is 6" tall, you'll end up with about 1oz per plant. That's hardly the maximum you could get. A good general time schedule to follow is 30 days for vegging (from seed) followed by the flowering period required for the particular strain you are growing.
If you want a good quantity of bud in the shortest time possible, look into an auto-flowering strain such as lowryder. These strains are unique in that they do not flower based on the light schedule. With auto-flowering strains, the automatically begin flowering when the plant gets to a certain age. Unlike normal strains, they produce the best results with a 20/4 light schedule from the time you plant the seed all the way to harvest. There is no 12/12 flip with these. Depending on which autoflowering strain you choose, you could be harvesting 45-50 days after you put the seed in the dirt.