Wrapping would speed up / shorten the time, also provides a higher moisture end result but at the expense of not having a crunchy bark. Note: wrapping, also known as 'the crutch', usually is done once the butt reaches an IT somewhere near 155-165°. Basically the amount of time should be closer to 7lbs but a little more given the mass in the pit. Be careful about the time/lb, butts can't tell time and they get done when they want too (stubborn things:D ). You are looking for approx 200° then you want to rest it 2 hours (or more) in an insulated container. Possibly in a pan foiled over with towels below and above. Remember safety, keep the meat above 150°. With an overnight attempt I would highly recommend you have some sort of wireless therm set up to monitor the pit temp so if it drops you will be alerted.
As a reference when time is important: With a 8-9 lb butt (using an internal temp probe), I smoke at 225° for 5-6 hours (the butt is sprayed with apple juice every 45 min starting after the 2nd hour), pull & double wrap in foil, into an alum pan and place in the over at 300°. Oven time usually is 2.5-3 hours to get to final IT. Then rest in cooler for 2 hours. Total cook 7.5-9 hrs plus 2 hrs rest.