allow the plant to grow 4-5 internodes, sets of branches ... you don't need to be in any hurry, it matters little, as to when it is done, as long as it is still in it's vegetation phase ... best reason for topping is to control height, I have done it both ways, many times, and I don't think the yield differs all that much ... it's "six of one, half-dozen of the other", in my opinion ... some strains do not like it, and can be stressed, supposedly, but I have personally suffered no plant damage yet, from topping ... :smokin: