For myself i feel the best time to start lst is about day 21. But i just look at my plant to decide when the time is right. I want 4-5 nodes on the plant. Any sooner seems too early since there aren't any lower cola's forming who need light. You can start lst at anytime after that I feel. But I want my cola's to grow at the same speed and form a Nice bush, not a christmas tree, so I do it as early as possible. But it is never too late to give your cola's more light imo.
As for damaged leafs, depends how damaged they are. But in your case I wouldn't remove any unless they're really totally lost since your girl is pretty small already