At 225 to 230 you should not need to reload any charcoal. Check the temp around 8 AM and if you are not through the stall then bump the temp up to 245. That should get you finished around 3 PM. That gives you plenty of time to rest. They are all different so maybe earlier maybe later.
I like to cook my butts at 235, but i am usually cooking two at a time and i try to schedule out for an 18 hour cook.