This is a hard one, and the answer is it depends! There are many variables, such as: how well your grill maintains an even temperature, how big the bird is, how often you open the grill lid, the outside air temperature, the bird's internal temperature, etc. Generally, It will take about 13-15 minutes a pound or two and a half to three hours to smoke a twelve-pound gobbler. The most important thing is to use a meat thermometer which can monitor the internal temperature and let you know when it is done, rather than timing it.