Are my plants too little for LST?

A Good rule of thumb is 6 sets of true leaves (count from 1st set of serrated), all healthy means you should have a decent root structure...nub them down then to the 3 or 4th node and they should rebound pretty fast. Give 3-5mm over the node to help stopping the main stem splitting when doing LST. Look like you only have your 4th set starting...give it a week or so and you'll find the plant is much better to handle the stress with less of a rebound period. Hope this helps in some way.

I like to wait until there are at least 4 nodes before I start lst. Seems like you are almost there, maybe another 5-7 days. When you do start lst, make sure you anchor the stem so you don't put strain on the root system when you are bending the main stem. Happy growing.