Yes, by changing to 12 hours so early, you have limited the growth of your plants. Also, by removing healthy green leaves, you have also reduced your plants ability to produce energy, further slowing growth. You should try to only remove leaves when they are yellow, for by the time they are yellow, they have served their purpose. Plants can not "channel" energy, all energy is used throughout the entire plant. Plants can not think about where the energy should go, there are also no energy highways with little policemen directing the energy. Bud sites that people think are being shaded, are actually relying on those "shade" leaves to produce the energy for the "bud sites" to grow. There is no way that the little bud leaves can produce anywhere as much energy as even just one "shade" leaf. This is why, in my opinion, "de-leafing" is so wrong. It is this simple - fewer healthy green leaves = less energy produced = slower and smaller growth. Each leaf is like a "solar panel", producing energy for your plant to grow. Less "solar panels" means less energy means less growth.
At this stage, you are pretty much stuck with flowering, but in future, give your plants a chance to grow a bit more before changing to 12/12 and you will be able to harvest more next time.
I have been cultivating cannabis for 35+ years and still learn something each time I grow, so as this is your first indoor grow, imagine how much you will learn this time and how much you will be able to use your new knowledge in your next grows. Growing is a fascinating hobby and a never ending road of discovery. Keep up the good work and soon enough you will be able to harvest some "I made it myself, with my own hands, in my own way" flowers. They always taste better when you grow them yourself!
Hope this helps...... Organoman.
P.S. - check out some of my diaries if you want to see how plants grow without any healthy green leaves being removed! It is as nature intended!