Before you jump into IF I would try to get more sleep. Getting only 6 hours of sleep a night is going to mess up your hormones and recovery and shift your body compostion to one you'd rather not have. Get more sleep first. Once you've got that down you can start IF. From the looks of it you do your workout in the morning.Most have found that the 15 hour overnight fast seems to work best for folks who workout in the AM. A good way to do this is to stop eating at 6:00 PM and break the fast at 9:00 AM about an hour after you're workout. In your case, if you continue to workout at 4:00-4:30 AM you should have your last meal at 3:00-3:30 PM and begin eating at 6:00-6:30 Am the next day. If I were you I would simply sleep more and follow the 6-9 IF plan, however, I'm not familiar with your schedule and it is very likely that you have no other option to awake at such an early time. In this case, I would simply push back my bedtime to 7:00-8:00 PM in order to get a good 8-9 hours of sleep. Also, what does your diet consist of right now. Before you hop into IF you're going to want to get the compostion of your diet in line. For the simplist explanation of what your diet should consist of check here: http://www.crossfit.com/cf-info/start-diet.html
If you haven't already established a clean diet composed of paleo/zone friendly food choices you're going to want to do that before even thinking of IF. If you have any questions feel free to ask.