i think it's better to do when there's enough side branching to take advantage, but you also can't wait so long that the stem becomes rigid. No matter what it is an incremental process.. need to keep leveling it out as sit grows until the base is the size you want it to be.
I have seen a plant display some funky leaves (single blades etc) from "too early" LST, but never have i seen one stall out, so probably safe more times than not.
What i would sugges for next time, shape the trunk a bit before you tie it down. bend it gently in 2-3 spots starting as slow as you can go without causing any stress to roots -- secure below where you bend so the only force is applied to the stem above ground. You can make a 90-degree bend a bit more easily that way. Use an anchor tie just as you did this time, then tie down the top to hold it in place - shouldn't take much after you've shaped it.
what you did is fine, but whiat likely happens is it bend a bit through the substrate due to the constant pressure. may or may not cause anythign serious, but probably tear a few early roots at the least. Even with your anchor, you can see the forces applied.. essentially a lever.. when you shape a 90-degree bend and anchar above the ground, it reduces that leverage. keeps it in place. Small thing, but might as well avoid some potential root damage / extra stress.