Lst , when to cut ?

You dont need to cut anything for LST, just bending the tallest stems and tying them down. But you can top once /twice and train those tops down using LST.

Are you sure you want to, first of all. Most of the true experts aren't big fans of cutting healthy plants. It's up to you, but analyse what the top guys do first. Here is a link for you to see what the pro's like Ed Rosenthal and Jorge Cervantes think. And best of luck my brother. https://www.cocoforcannabis.com/community/photons_corner/to-defoliate-or-not-to-defoliate/

Topping and lst are 2 separate things mate, lst (low stress training) is were you tie branchs down for better light and airflow to your plant.... if your question is when do you top your plants.... my answer would be... only top after the 4/5 node on your plant and never take too much of it away as this could lead to stress... i hope ive helped you mate happy growing ,🙃🙂🙃