While the name LST implies that it's a low-stress training technique for your cannabis plants, it still induces some minor levels of stress. Anytime you're preventing the plant from growing in its natural direction, you're introducing stress. For this reason, you need to ensure you get all the training done in a vegetative state. Training while the plant is flowering reduces your yield. Typically, most plants stop growing in size and height when they enter the flowering phase. Therefore, you should have all LST wrapped up on your plant halfway through the vegetative process.