all that info is paramount. I would say you will be fine. Have you done any of the mods for chargrillers? If not, you will have to rotate them butts a time or two untill they get to the 160-170 mark, then foil, and take to 200. Normally I would say, get em on at 4 am, and keep the grate temp at or near 230-250. If everything goes normal(hopefully) you could have them ready for a cooler rest by 4 pm, pull by 5-5:30, serve at 6. But thats in a perfect world, and no one lives there cept me!
It is far better to be done early, and then just wrap and towel,/cooler for 2-3 hrs, than to be running late, and then get no rest ( the meat, not you) before serving.
Hope this makes any sense!