You can start LST as soon as your branches are long enough to bend. (5-7.5cm should be good)
Just don't tie a knot around the branch. Tie your string so it has a loop at the end. And just pretend you are threading a needle with the other end, and slide the big loop on your branch where you want it, and attach the other end of the string to the pot with paperclips or something.
Pipe Cleaners also work well, and are faster to adjust. They also work well with paperclips on the edge of the pots
Just don't tie a knot around the branch. Tie your string so it has a loop at the end. And just pretend you are threading a needle with the other end, and slide the big loop on your branch where you want it, and attach the other end of the string to the pot with paperclips or something.
Pipe Cleaners also work well, and are faster to adjust. They also work well with paperclips on the edge of the pots