Its not too late - but…Topping is usually done to increase the number of branchings so you have more colas - not to shorten the plants height. Same with LST and HST (topping). They work much better when you start early though. It depends on how soon you want to switch to flower. It can take weeks to see any results and slows the plant growth in the case of any HST.
You could do scrog on the shorter plants maybe, but the whole purpose of scrog is to help fill up a tent - not to make more room.
if you need to keep them out of the lights, I guess you could top them, but a better way might be to do some “super cropping”. You can google that for more details, but basically it involves bending the stem over 90 degrees without breaking it. That forces the plant to grow sideways. Keep in mind that will also cause extra new side stems, and the stem will usually turn right back up in short order unless you keep it tied down sideways.
What exactly is it you need to do?
I dont think you need to defoliate yet. Wait till it gets more crowded.
I start training - lst, and FIMing - when they are a max 6" tall. I use a scrog screen, and train the plants to grow UNDER the screen until its about 75-80% full, then switch to flower. I do that so I can fill a tent with fewer plants and the max number of colas.
This is a single plant in a small tent using a scrog screen to fill it up.
Not my best use of a scrog screen, but gives you the idea. I should have started sooner when the plant was smaller.
