I have around the same wattage lighting as you and I have never had any issues with leaves burning from it. Does kind of look like a deficiency starting, I almost wanna say it needs more nitrogen but don't take my word. You should PH your runoff and start with a flush, that's the best way to correct most problems. As for late flowering... I mean who cares! XD The bigger the plant the bigger the yield :) No clue why it's taking so long ;p. I don't think you over fertilized but you could of, a flush will correct it.