What kind of altitude/elevation are you at? Higher altitudes take a bit longer. I did an 8 lb butt a couple months ago and it took 18.5 hrs - no foil.
Here's some info for ya - [color= rgb(24, 24, 24)]A Guideline like 40-140 in 4...aka the Rule (less letters than Guideline) is, Easy to remember, Provides a margin of Error, Has been gleaned from information provided by Multiple sources, including but not limited to, Professional Food service organizations, The American Culinary Federation, The ServSafe program, the USDA and Food Service Professionals with Years of Experience... Is, " 40 to 140*F in 4 " written down in any Government Food Service Law Manual, or Word for Word on any fore mentioned Website or Charter?...NO...But it Has been adopted by This Site and others to protect it's members!..[/color]
That being said the outer 1/2" to 1" of any whole muscle meat falls under this guidline . So if the outer 1" has reached 140 degrees it should be okay.
If the butt was injected or cut or deboned then it would not fall under the whole muscle theory and would need to reach 140degrees internal to meet the guideline.