Overnight is for sleeping, unless you work the graveyard shift like me!
Prep your meats the night before, get your cooker ready and ring filled with charcoal, get a good nights rest, wake up refreshed and fire that bad boy up and cook that butt hot & fast at 275-325*. 6-6.5 hours total YTMV.
Don't worry about temp fluctuations and check it for color and an internal of 160* then wrap that butt in foil with some brown sugar, some rub and a stick of butter and toss it back on the bullet and check it in 60-90 minutes. When it hits 200-212* drain some of that liquid to mix with your favorite sauce and throw that wrapped butt in a cooler or Cambro for as long as you can stand (or just before your hungry guests arrive) OR NOT!
You can cook it or warm it to death! Just sayin'