Hello
You start fairly young, and then it is an ongoing process the whole grow basically until mid flowering when it's finished it's stretch and is focused primarily on making buds...but even then you will usually have to tie the branches to bamboo stakes for support etc.
So i would check your lst everyday or every 2-3 days. The branches want to escape out of your bondage, they're reaching the light etc so they'll continue trying to grow and you'll have to continue to tie and retie often.👍