Smoking a brisket this Saturday - first time

Got a 12 pounder from the butcher and I'm going to smoke it on the offset smoker my dad gave me. Never done a brisket before so I'm both excited and terrified. Planning to start early morning, keep it at 225 degrees, and just let it ride. How long should I expect? I'm thinking 10-12 hours but I've read wildly different times online. Should I wrap it in foil halfway through or leave it naked the whole time? Looking to impress the in laws on Sunday.