"Generally" a fatty will take around 2 to 2 1/2 to bring the internal temp to where you want it. This is just my opinion from running the smoker at 225Âº and bring the fatty temp to 165Âº in my experiences.
Mine took a bit under 2 hours to reach and internal temp of 162*, but my set up isn't exactly stellar either! In a more temp controlled enviroment I think things would smooth out a bit and give excellent results. Gonna work on that smoker today! That grill is fine for burgers and steaks, just dosen't cut it for my smokin needs!