Stealth Grow Bubble...how long before switching to 12/12 flowering

say you get 2-4 females out of the 6 you start with and have a tent 5'3" how tall do you guys think the plants shuld grow to before putting them into flowering so as to not get too tall or heavy during flowering?

maybe 18-24" (with the bubble kit and light there will be around 3' of space for the plants i figure)