I would also say it's a personal preference when to top. Honestly you can pretty much do whatever you like to your plant as long it is in veg without doing damage, (as long as you don't go all out and kill it :b). Topping and general plant training is all about shaping your plant into a form or structure of your personal preference 😉 I get that some of these things might be a bit hard to grasp if you don't have much experience in growing plants or weed. I wouldn't recommend you to do topping before you have grown out a few plants naturally/LST. Neither would I recommend to top if you depent on the yield of the plant and isn't sure what you are doing, simply just to avoid reducing your yields 😊 Personally I don't top before I fell the plant has put out some solid roots and started growing properly, not that you can't do it earlier you just have a risk of hurting the plant to the point of no return 😉