Welcome to the BBQ-Brethren!
Time and Temperature, brother. Lower temp will take more time. You just need to figure out how much of each you need. That depends on your cooker and the size of the butt or butts.
If this is your first foray, plan several hours extra. Then when the butt is done, wrap in foil, wrap in some clean towels and put in a cooler. For more than an hour or two, warm the cooler with hot tap water first. Also be aware that it will continue to cook in the cooler so pull it accordingly.