when you top

nothing grows from the cut right? just the sides?

Yea its neat what you cut off in 1 or 2 days turns into 2 new main coals instead of one

when is the best time to perform such things?

before flowering is the best time to top, you can top all of your tops and double your colas. each top that you clip off will result in 2 tops instead of 1. the next 2 nodes will shoot up within 1-2 weeks, so its best to do so atleast 2 weeks prior to flowering. i usually do it 3 weeks before so the tops get nice and big, either way - veg is the time to top, it will hurt your yield to do it during flowering.

Never ever top during flowering. Judging by normal plant growth patterns, I would do it no later than 3wk - 1 month prior to flowering. You want your new "tops" to have a few nodes on them.

I also wouldn't do it before the third node on your main stem. Although I know it can be done for EXTREMELY small grows.