When should I lollipop?

No lollipops just defoliate from the bottom and centre

This is something you need to feel out. Knowing how much vertical growth you expect after flip is very helpful. Knowing the depth at which you get good solid buds is also helpful. i'll tell you what i do, and know your mileage will vary. I like to prune off unnecessary growth along the way. the less developed it is, the fewer wasted resources. I can do this because i plan backward from a target canopy. I want 2.5-3 colas per sq ft. depending on number of plants and area i am growing in, i work all that out including how i'll top or train the plant to get there. I know exactly what side branching i can remove as it happens. I am a bit conservative about stripping lower growth on the 'important' branches, so there is a bit of work to clean it up at flip to 12/12, or there abouts. Some plants stretch a bit more than others. The ones likely to grow a bit more in flower i wait 7-8 days into 12/12 cycle, then i prune to 2-3 nodes plus the growth tip on the 'keeper' colas. The expected shorter plants i do this right at flip. I expect/want 24" of vertical growth from either point, a few inches more is fine too. If the colas are well-spaced, it's solid nugs all the way down. The bigger stretchers get trained horizontally until 7-8 days beyond flip to 12/12 too. This is pretty hard to guess without a known batch of seeds with consistent structure or, better yet, clones. DLI + CO2 = yield (relative to genetics). this is why after a certain point packing more colas per sq ft does nothing but increase proportion of larfy buds and increase your trim time. As long as your canopy covers the entire area and makes proper use of all the light, the yield will come. Sometimes it doesn't look like that will happen at flip, but these plants still have 4+ weeks of vege growth and light training after flip. Have faith it'll fill in.

I do the main lollipopping about now, then a follow up lollipop in about 3 weeks again just to tidy things up. However, it is not essential, especially on plants this size, but if you have 6-7 foot monster bushy trees, lollipopping can same a lot of trimming time after harvest by not having to deal with small spindly inner growths. Removing the first couple of nodes on the branches, at a point closest to the main stem, down low on the plant won't hurt, but it is not essential.

you should lollipop, when you know wich branches you want to keep. i do it in 2-3 week of flower when the stretch ends and i want the plant to focus energy on the bud building 🥦