Welcome to AFN. Most people don't reccomend triming at all. These plants grow fast and need their leaves for light absorbtion. I am growing 4 that are all the same strain and 2 topped out at 25in, one at 20in and one at 15in. The shortest has some of the best buds. Your grow looks good and with that much light you should have a good grow. When you switch to bloom nutes, after vertical growth stops, you will see the buds start to fatten. As the lower fan leaves yellow out you can trim them and let more light into the interior. I move my plants every night so that they get light from all angles. I understand that temps below 50f are bad news.