Smokers run at a very low temperature so the first hour or so is spent just getting the bird up to ambient temperature. I throw my bird in the oven for 15-20 minutes just to get it jump-started before I bring it to the smoker. Can you fit a bowl of liquid under the hood of you cooker?
As far as timing, I've done em for 4 hours and 6 hours and couldn't really tell the difference. When the wife tells me it's dinnertime it's done.