When to start LST on my autoflower?

So, your plant is a tad too short when compared to the rim of your container. I would wait for another set of leaves. For LST I recommend you start slowly and give the plant a lot of support. For example be sure the stem is supported at the base (until the first set of leaves, the cotyledons) and bend only the top. Now the top should be bent below the other nodes you want to grow bigger, BUT BE CAREFUL and do it slowly...bending it gently every few hours to a day until you can bend it to the point you want Then just keep bending any branch that is taller than the rest. LST is very effective of breaking the apical dominance of cannabis and spreading the hormones around, so instead of one giant main stem you can create many side branches, although they will all be smaller than an untrained plant. But great to keep them bushy and small. So just give it a try.