Daum, keep a temp probe in the meet throughout. That will be your guide as to when to begin checking foe tenderness. As Phil sail the best way to tell if your BB is done is by checking tenderness. When the meat hits 180-190, begin probing for tenderness. You want the probe to enter and exit effortlessly. (Kinda like a cake test) If you're not sure if it is finished, probe the meat closer to the edges first as it will cook/get finished first. If the probe feels the same (or relatively similar) on the in the center of the largest section of the butt as it does closer to the outer edges, the meat is good to go. Don't over think it, as butts are pretty bulletproof. Get it on the smoker and enjoy the ride!
Good luck,
Tim