Nice plant big block Chevy. Personally I would flip to 12/ 12 an start out by cleaning up around the bottom of the plant closest to the pot Will allow better air flow. I would snip a few leafs, but don’t go crazy for better light penetration.
Good luck 
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Time to flower for sure, and do just exactly what kellydans said.
Why is growing taller not good idea?
Flippem. She is gonna stretch. You will be shocked. I also would defoiliate a LITTLE interior for air. Letem stretch then a final prune couple weeks in flower. They will have finished stretch and you see where they will be till the end. Look great. Just remember this…flowers do not feed themselves. No fans…no food for flowers. Overpruning affects yield. On the other hand…too much thick air restricting foliage promotes mold. Happy median. Just my thoughts.
I hope you have room to get the light higher. You will stretch to it. If not then we can work on some supercrop or tie downs or some other way to shorten her up without removing anything. She is gonna give you a large yield. I see 10 oz minimum from those monsters. Probably 1lb plus if work it right.
You’re going to run out of vertical space. 6’ is not very much room for cannabis.
Healthy looking plants Growmie and agree with @kellydans. You’ll most likely end up super cropping most of those tops to keep them from growing into your light 
