Your plants look very healthy. We thought we could get through our entire grow in 2 gallon pots, but they became root bound. I would suggest doing the flip to 12/12 before plant is the size that you want it. It will continue to grow upwards and outwards after the flip but before it starts to bloom. If you let them get too big before flip, I fear you may need to transplant. just my 2 cents and every grow is different.