Smoke at 225* until the internal temperature reaches apprx 192*. At that point start checking with a temp probe (should slide into the PB like going into soft butter. Any resistance, let it cook some more).
You should be looking at roughly 1.75 hrs/lb cooking time, give or take. Because of the variable in finish time, plan on finishing it a couple hours early then FTC (wrap in heavy duty
Foil, wrap in a beach
Towel, place in a
Cooler). It'll stay hot to touch for several hours. By planning on an early finish and FTC, you have some flexibility in case you get a stubborn hog, and it takes longer. That way, if it does take longer, dinner won't likely get delayed.
Make sure to read Smokin's
Pork Butt 101.
Enjoy your barbecue.