People do that but it will only work if they are sexually mature....most of the time alternating nodes will signal that the plant is sexually mature. Then you will usually get preflowers. If you flip a plant that is not sexually mature then you will do nothing but deprive that plant of 12 hours of light for every day they are flipped. They will stretch and get gangly on ya. I usually see alternating nodes around 4-6 weeks. If they get alternating nodes and I can't pick out the preflowers I do flip them to get them to show occasionally. IMO flipping them before they are sexually mature is setting yourself up for problems down the road grow wise. When I invest months at a time into these girls I want them to put out for me. Tall langky plants don't do well. Jmo
I think something is wrong here--plants that have been vegged for 2-5 to 3 months should be shooting out preflowers everywhere and be monsterous sized plants. Can you get us some pics and tell us more about your grow? Is there a reason that are you vegging with 16/8 light instead of 24/7?
What you are looking for a is a little football shaped thing at the base of the node with 2 small hairs coming out of it. I cant tell if its distortion in your pic or a female preflower. You need to take better photos or will have to judge by yourself.