Any where between the 3rd and 5th node, all depends how you want to grow.
There is a large debate if topping autos is ok or not. I have topped some of mine with success and some were failures.
I would suggest playing aorund with LST more vs HST "topping" and get a feel for how autos grow before moving onto more advance growing techniques.
growdiaries.com/journal/how-to-do-low-stress-training-lst-on-cannabis-plants
vs
growdiaries.com/journal/how-to-do-high-stress-training-hst-on-cannabis
Good Luck & Happy Growing!
***disclaimer, multiple people are answering all questions as there is a contest called GOTM, when a user is selected as the answer they get a point. Please see the contest page for information regarding the details:
growdiaries.com/giveaways/GotM-August-2022
Please note, when you reply to anything on the questions part of Growdiaries website, no one will be notified of this. Not even if you use a "@" tag in their name. Best to reach out to them in DM using your inbox, it can be found in the bottom right hand corner of the site. It's the small paper airplane button, it will be highlighted green if you have new messages***