Its up to you, I have topped as early as second node. And topped every week or two after until desired amount of branches are reached.
When you do top you cut above the node so you leave the leaves on and have a flat surface for new growth.
You'll get to the point of just pinching off the tops when you get used to it and before you know it have mother natures manora.
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Bear in mind each top/pinch causes stress, some girls take it well and grow faster some will not take. Know your strain.