So thinking of turning to the 12/12 cycle now as the plant is quite big for my small grow tent, also should I defoliate now get rid of a few of those big fan leaves?
You should be able to get another weeks worth of Veg. Look at my last few grows as I use the same tent but the shorty version, it will give you an idea of how much more space is going to be taken up by the plant once its flowering.
This plant will double it's size when switching to flowering. So you can calculate yourself when it is time to do this. You want to keep some space left for a good airflow around the entire plant. Space to work with for yourself (training for example) And enough space between lamp and plant. Happy Growing Buddy! 💚