When start LST?

i'd wait until you have at least 7-8 potential vertically growing branches. bend it over between the axillary growth so you don't have to cut any off and then lst it outward fromt here. keep it level by breaking apical dominance of any that outgrow the rest.. temporarily bend it down until other stuff catches up. how long befoer you let the terminal grow vertically is the question and that is impossible to predict with autoflowers. once you see preflowers, figure 3-4 weeks of vege growth left. an XXL auto will have a longer period of vege growth altogether, but probably on similar timeline once flowering phase starts.