yeah do NOT give them any more nitro! look up nutrients that stimulate flowering, im pretty sure its P and K!
Im sure advanced nutrient has a 50$ bottle of something for you to, look around!
light dep helps too, but I dunno how you could do it with a giant plant like that, giant black trashbag works, but you will cook the plant if its in the sun.
Best off feeding it its flowering nutes and see what it does, if you gotta harvest early well, you gotta do it.