You have to rub it then wrap in in plastic wrap for 24-36 hours. Then wrap it up in heavy foil and cook it on indirect heat, turning it every hour or so. I would say its going to take you 10-13 hours depending on what kind of grill you have. You want the temp to be about 250 deg.Cook it till it gets to about 180 deg. Alternatly you can wrap in foil abd out it in the oven at 200 or so and cook it till its done. Take it off and keep it in the foil till it gets about 190 . Let it cool off in the foil till its cool enough to handle. Then open it up and shred it right off the carcas. Serve it with some Hawaiian Rolls.
Let us know what you decide to do and how it turned out.