I just switched to 18 hrs light schedule this past...

If you just switched to 18 I'd wait a minute. How large is your grow space? Because you can plan on the plant usually doubling in size, so understanding how much room you'll have to work with in the end is a good way to know when to switch...and dont forget to account for light distance and anything else in there. I see you're at 16 so if she stays at the 2xheight not more or less then she could be around 3 ft. However if you tie down now it'll be easier than during flowering and it'll give you more room and a flatter space for colas. Best of luck. The plants looks really healthy already. Happy growing

I would personally get a net above them a little lower than the height they are at now. Top all the plants to put most of the energy to those small side branches. And start weaving and bending them under the net untill it's nearly full. Then flower. And continue to bend under for at least 1 more week. They look a little stretched so get those fluorescents lower down and watch them bush out!

Whenever you want but remember it will double/triple in height, so you might want to do it soon if you're limited by height. I'll be around, good luck with these beauties!

Going by your current height (16 inches) I would switch and do some serious LST, or your plants are going to stretch over 3ft.

I switched mine at 18” and now it is well over 3ft tall. I would say it all depends on how much space you have available.