First off...don't freak out. Pork butt/shoulder is a VERY forgiving piece to smoke for a first timer. The window of time when it's considered "done" is very very large.
The reason we hold off on probing the meat in the first four hours is primarily to avoid injecting any surface bacteria deep into the muscle of the meat. After four hours the surface of the meat is cooked enough (higher than 140 degrees) to kill off almost all bacteria, so then it is safe to probe. (the inside of the meat doesn't contain any bacteria unless it is introduce by human tools, like a therm probe injected too early). This is also why some folks on the forum refuse to inject their pork butts with marinades and such, since it takes the inside of the meat a lot longer than four hours to cook past 140 degrees.
Lastly a 12 lb Pork shoulder will take about 18-20hours to cook at 225 degrees. So it's kinda moot anyways to probe the meat for those first four hours because it's obviously not going to be done yet, so why bother checking. That should save some battery life on your thermometers.
Let me know if you have any other questions.