Hi DQ.. probably a combination of both. In my Smokette, it doesn't seem to matter if it's got two or three small butts or one butt. However, I find in my Amerique it takes longer than my Smokette times.
Do you have a probe thermometer with a cable for remote reading? If so, use it. The meat seems to be dependent on a lot of things like amount of fat to render, and maybe overall thickness.
You might go to Smoken Okie's tutorials. Go to the Cookshack site and click on Community and then on Smokin's Guides. You are probably looking at about 2+ hours per pound.