For that last butt (6.5 lb) I let it get to room temp for about 30 minutes to an hour (can't remember, notes are on other phone).
I put it on the smoker set to 275 (trying a higher temp as I read here it went fast and was still good) and inserted the probe. IT was just a couple degrees above 40. 3:50 later it hit IT 140.
My concern is that input 3 butts on and they never get to 140 within 4 hours.