Haha sorry bout that, sounds like you fit into the second category then, then people with more experience. Glad to hear you aren't just another noob who went in and decided to cut things off bc he didn't like how it looked or some other cray reason. With that having been you're first post I was wary. Since you know what you're doing then you'll have a much easier time than most do on their first few grows.
Regarding when to switch to 12/12, if your plant was from clone then it's already mature and you should be fine at whatever height you deem appropriate, keeping in mind it'll likely double in height. If it was from seed then you'll want to look for preflowers and alternating nodes. Either of these showing up is a sign that the plant is mature and can be flowered when you choose to switch the light schedule. If the plant reaches around the height you wanted to switch and it isn't yet showing either sign of maturity then you can go ahead and force flower it but it will take a bit longer before. The first week or so of 12/12 it will still be in veg and may stretch more before showing preflowers and beginning flowering.
Is there any reason you're going with lollipop as opposed to any of the other forms of training? Again, apologies if I came off as insensitive before. Here to help if you need anything.