You cant really mimick what your friend is doing in terms of flowering based on his plant heigth. I am sure you and him do not share the exact dimensions of the flower room. So, look at your flower space and with your existing plants multiply by two or even three and it will give you a more general idea if you can extend your vegetative period prior to photoperiod switch. Interesting never read that before about not topping. My last cycle was purple kush and I did not top and it became a bush naturally based on the genetics of hindu kush and afghani purple. One strain that comes to mind not to top because it affects yield is the Chronic strain. Some also say dont prune autoflowering plants. Havent done too many of those to share my experiences with those types of plants.I'm at week four of veg and most of my ladies are 12-16 inches tall. My friend does his to 2 feet before 12/12, think I should hold off another week before switching or put the in 12/12 on schedule? Ps. I read somewhere not to top Purple Kush, is this true?