Who are you looking to trade with and for what? I'm assuming you meant something else but I'm not sure what you are asking? When to flip lights for flower?
I just re-read the title and I think you're asking about TRAINING. Haha, that'd make more sense.
Topping is training. If you have limited room above the canopy, then there are multiple measurements to consider to decide when to decide to flower it. You can LST, gently tie down branches to the sides to bush it out and prevent it from getting too high. There is tons of information on it, just do a search if you need more information on it. Good luck!