How long you cook them is all dependent on the temp. at 225 you're probably looking at about 90 minutes per pound. If you kick the heat up to 250 - 275 you'll be closer to an hour per pound, and if you go to 300 - 325 you can probably get them done in 5-6 hours.
Don't use internal temp as you guide for when to pull them off. Use sight and feel. It takes a little to get used to, but when they are done the meat will have pulled back from the bone and the bone will pull out cleanly is you tug it or it will wiggle easily. Also, when you stick your thermometer probe in it will slide in with little resistance. Do this in several spots.
I like at least two hours rest for butts. Allow yourself plenty of time. If they are done early you can just rest them longer. I've held butts in a cooler for 6 hours and they were still too hot to touch. I preheat the cooler with hot water, dump the water and dry, and then lay doen a layer of clean towels, put the butt(s) in and then stuff in more towels.
It's been a while since I've cooked butts in my BGE, but when I did I would put the fat cap down since the heat source is below. The platesetter in the Egg radiates a lot of heat. I'm guessing that the indirect element in the Kamado Joe (not sure what they call it) would be the same.
Finally, if you go with a higher temp watch the bark color. If it starts to get too dark then wrap the butts in a couple of layers of heavy duty foil and toss in a little (1/2 cup) of liquid .
OK... Now finally...
Have fun!
