Mike, timing was no big deal to me before I came to the realization that there was no way a perfectly cooked pork butt would get any better than right off the pit. I'd hold bbq hot for up to six hours or even more in a hot cooler and ignorance was bliss....and my bbq was quite often a little (or a lot) dry. Now, timing is one of my biggest challenges, and no, I don't have it down. Quite frankly, it's a good case for an ATC, but even if you can keep temps fairly consistent cook to cook though, you're gonna have a hot side to the cooker or another variable that can come into play.
Heck, back to the topic though, most folks say that every piece of meat is different, and then some would say that meat has gotten fairly standard. Well, if it's a myth that every pork butt (or brisket) will cook differently, and if every eight pound pork butt takes about the same time/temp to turn it into bbq, then we needn't to go poking every butt on the cooker then....other than with a Thermapen for a certain finished IT* reading...like 195* or whatever. Well, that's not the case, and it's done when it's done. Right?