Hypothetical question: Let's say I have a few seed from a tiny bag of common schwag, probably sativa. Let's say I germinate a couple, and put them directly into 12/12 from germination. I know that this is not advisable, but I don't care. Question: When they get big enough for LST, can I begin it, even though they are in flowering stage? This is a purely hypothetical question, as I don't have any such seed or plants on hand. Thanks.
You can LST starting after the plant has its 4th or 5th node. You can LST at any point during the grow, including later into flowering, just realize that the stems will be getting thicker and stiffer as the plant gets older. For later LST you may not be able to get the bend you want all at once, and you don't want to break a stem/branch, so tie it tight and leave it a day or two then after the plant adjusts to the tension you can re-tie, continuing until you gradually get the plant bent.