If it is a photo period. After you put it in 12/12 you can trim all the side branches about 2-3 weeks in 12/12. The reason I say to do it during flowering is that you are going to want to let it stretch first because that main branch will become one long cola and you don't want to stunt that growth. Wait till the flowering stretch is over then cut those side branches. You can root those branches into clones also. You may have to clean up new growth shoots after 3 weeks if they grow back.