You should always try and do your transplanting before you flip for flower. If your plants are not sexually mature they will not flower, they will continue to veg but with only half the amount of light as they will be sitting in the dark for 12 hours every day until they become mature you can tell if your plant is mature by the nodes on the plant. If they are alternating it mature. Hope that helps.
I agree with Hamster. While you can put anything into flowering anytime, they won't flower until they are ready regardless of the light schedule. If you want to flower small plants, it would be better to do it with clones, which are biologically the same age as the mother they came from.