Keep the hydration up and this will help keep your blood thinner on the day to day. 16 wks would be fine. It's not totally true that you dont get an effect untl 6 wks in. It does take that long for your blood levels to reach a peak, but you are getting an effect from day one. For your goals, I imagine you will start to see improvement around wk 2-3. Its that after the levels have peaked that you will start to see more of a visable result. For athletes, you can get better results in your sport much sooner and at much lower doses.
If your Hematocrit gets too high, your blood will be too thick. At this point, cardio goes down. Your heart has to work a lot harder to move your blood around. You'll find that you're getting out of breath. Thats a sure sign that it is way too high. This happens becuase O2 isnt moving to the muscle fast enough due to the thicker/slower blood. Then if you donate a pint, you'll feel 100% the nex day. I would get your hemat level checked about 6 wks before the contest. If it is getting to the higher end, get a pint taken out then, 4-6 wks out and you will be fine. It will have gone back up by the event.