I've found a whole butt seems to take almost as long as a half. In my 1400, I set it at 180 for an 11 pm start, crank it to 225 at 6 am on the way out the door, and i'm usually in the stall or just past it at 4 pm when I arrive home, and adjust dinner time from there, so about 18 hours is what I plan for, but at a little lower temp. If I need a temp hit upon arrival home, I can crank it all the way up.
Things like a butt with a higher fat/collagen content do take significantly longer than brisket, which has a denser, less fatty content.
I believe in catch and release fishing. I don't want to EAT 'em all, I just want to GREET 'em all!