When should I flower? Recommend some techniques

Here are my ladies, what are your thoughts. Should I start flowering them? Anyone want to recommend some techniques to optimize yields? Not to sure how I cut put a screen in there without messing up my panda film walls. I was thinking of using a tomato case upside down atop my pots and bending the arms to form some sort of beam that I could fasten my plants to, so I could get the plants stalk growing vertically in order to get my flowering tops all uniform. these pots are 3 gallons. I am kind of worried about the yield

From what I've read flower at 12" height, and you'll have around a 2' plant, longer you veg the bigger the flower. But I am new as well.

Does anyone else grow in 3 gallon pots?

Mine are about three gallon.

It's hard to see exactly what you have going on but if you want to train them, do it in veg. Did you top or lst? If not, then def veg some more and train.

That's what I have but most use 5s. But you should start small and move up anyway.

My grow now (journal in SIG) is a 3gal pot, wish I had switched to 5 before flower

Look into topping, lollipoping, and LST.
You are going to want to start flower when your plants are a little less then half the finished height you want.
Most plants will stretch 1 to 2.5 times there size in the first two weeks of flower.
So a one foot plant will end up 2' to 3.5' two weeks after flowering starts.