I have no concept of time. I would always be too early or worse late. Still, I will, out of habit, show up fifteen minutes early everywhere I go. How I learned to manage it was by using my smartphone. I got two apps, a timer and an alarm app that allowed for notes. I would set my alarm for thirty minutes before I had to leave and I would use the timer to allow a set amount of it depending on the task. I have a habit of becoming absorbed in things and before I know it, it's the only thing I got done. After some time doing this, it started to program my brain to be more conscientious of time and now, I only need the timer still. For what it's worth, at least I am always early. As far as complete correction? Maybe hypnosis? I hear good things, other than that, it's just about training your brain.