In all honesty, as many as you want, it doesn't really matter.
Depending on the amount of space you have, anywhere from 4-14 nodes works well.
I usually wait until there are 6-12 nodes, and it all relates back to the structure of your plant.
Sativas with their wild growth 6-8 nodes and Indicas with their more compact growth, 10-12 nodes, is what I do.
Hope this helps,.............
Organoman,