I did a party a few weeks ago and I pulled one butt at a time as needed. That way the whole butts kept their warmth until I pulled them. I think doing this and keeping them in the chaffing dish is a good idea.
Thanks, Dwain. Glad someone else posted the pulling as needed preference, and didn't you mention using your bullet as a faux cambro somewhere recently?
I had to run after answering the OP last night and posting the Chris Lilly video, but I really wanted to stress that pulling just prior to serving is simply the very best way to go if you can pull it off, no pun intended.
You can certainly wrap and hold as Bill suggested, but the crispness of the bark can be preserved if you can pull the butt off the pit and break it down right before your guests, as Chris Lilly demonstrates in the video I linked in my previous post. You can almost hear the oohs and aahs, but you don't have to break out a big blade and chop. Just break down with gloved hands or run Bear Claws through the butt real quick. I'd just put the butt in a pan and not even cover before pulling unless there's flies, because I really don't think it needs to rest very long. (It's more of a cooking issue if you're mainly resting to soften up bark, and I'd ask why not just foil during the cook to begin with if tough bark is an issue.) Anyhow, I find ten or fifteen minutes uncovered should be plenty to let some steam off.
Anyhow, I'm certainly not a pro at this kind of serving and and thankfully, still learning as I go. I've pretty much always used foil either during the cook and/or after. As I've mentioned before, my first wsm cooked butts were always done overnight on my old 18.5" at 225-250 with water in the pan for 14 hrs+, and held hot wrapped in foil in a hot cooler for however many hours needed. They weren't as moist as the ones that I remembered cooking by day off my old drum and offsets, though. So I started cooking by day and foiling them to speed up the cook, because it was simply hard to maintain more moderate temps with a full cooker on my 18.5", even without water in the pan. But then I started cooking on the 22.5" wsm last year, and especially with the extra top vent, more moderate temps and quicker cooks are now MUCH easier. No more getting up at 3 or cooking overnight unless cooking for a luncheon!
Timing and temp control is everything though if not wanting to hold long. Targeting 250* at the grate center seems to work pretty good for me and make for roughly a 12 hr cook. Not as predictable as cooking with foil, but obviously easier than at lower temps to get through the stall. (Yes, I monitor one butt with a probe.) Honestly though, I crank up the temp a bit if I think I'm behind, and then shut down the vents a bunch toward the end once I feel sure I'll get it all done on time. Obviously, a dry pan helps with temp control, and thankfully, the wsm holds moisture well, even with a dry pan.