if you want to pinch the top for doubling the main cola...i like doing it on the 3rd or 4th node early in seedling stage. this will give you 2 or more main stalks instead of one plus makes for easy training to grow along the ground surface. also search "FIM" at marihemp and overgrow...your uncle may have been talking about that practice. i've never tried FIM myself (on purpose) but supposedly it increases production by pruning lower branches in a special manner...all the info on it can be found with a search...