You want to let the butts rest wrapped in foil in a cooler for at least 30 mins before you pull, once it's pulled, it's ready to eat. It's a matter of personal preference if you want to mix in some sauce and/or offer it on the side.
Personally I recommend Steve's No 5 sauce on the side.
Thanks guys, I think you've both answered my question. By adding the sauce after it's on the bun, or serving the sauce on the side, each individual can adjust the taste to his or her own liking. I've had some mighty fine BBQ where I know the pork was seasoned after it was pulled, & I just was wondering how they did it.
Stephen, I have also had to do cooks a day early. I have (and no one cringe here) put the refrigerated pulled pork in a crock pot 2 hours before serving with a little apple juice or chicken stock and it was great. People could eat whenever they wanted. IMHO it did not sacrifice the taste at all.
Stephen, I like to let the butt rest for about 4-6 hours double foiled in the cooler. Once pulled after the allotted time, I sprinkle some left over rub and then let the guest decide on their sauce. My personal favorite was recommended by Keri below.
Thanks guys, you've been a big help. I've had really good luck with my ribs, but my goal now is that mouth-watering pulled pork sandwich that you run into at some little out-of-the-way BBQ joint.