I would top them when the around 5-6 node and you know you have a strong root system. Once your plants have recovered from the topping you can top again and again. Just make sure you wait for the plant to recover each time. If you are look for a completely level canopy I would recommend using the screen of green technique along with the topping method. Good luck ๐ช
I always wait for 5-6 mature nodes then chop the top. You can either trim the lower nodes to mainline or you can start LST at that point to achieve a even canopy and uniform nugs.
Happy growing and stay high! ๐๐๐๐๐ค๐จ