NO mop needed (it will mess up the bark)
For a 7.5 lb butt - I would not expect to be eating for at least 14 hours (including rest time). Basically - if you want to eat it for dinner (7:00 PM) you better put it on the BBQ pit by 5:00 AM or you might not make it. ALL my Pork (bone in) butts have taken about 2 hrs per pound to reach an internal temp of 195-200*.
Don't foil it - no need.
Keep your pit temps around the 230-240* range and you want the internal temp of the pork butt to be 195-200*. Then wrap in foil and towels - set it in an ice chest to "rest" for at least 1 hour. Then take it out and pull it apart for serving.
Rockin the UDS - every weekend