Trucky1008 is correct. The cook time can be effected by the configuration and characteristics of your particular smoker. There are also other factors that will have an impact. The weight, fat and collagen content, dimensions (thickness etc)and also, even within a given cut, for instance pork butt, two identical pork butts in weight and dimension might cook differently just due to the idiosyncrasies of that particular piece of meat. The best plan is to use an internal thermometer to get you in the ballpark then use the poke and probe test to assess the final doneness.
Finally, the Somkin Okie quote that Trucky gave you is some of the best advice you'll ever get. We all live by it.