How long you apply smoke comes down to 2 things. Your personal preferences and the cost to use the wood through the entire process. Most will tell ya not to use the wood for more than half the time, mostly because after that the meat doesn't pull the smoke flavor in as easily, the other reason is the cost of the wood.
If I am using oak, cherry or apple, I'll use it all the way through the entire smoking process. Only reason I do it is because I love the aroma and the wood is free. It grows here on my land, so I never have ran out. I have run low before and that isn't a good feeling.
The mesquite and pecan I use I have to buy unfortunately, but I know a place that sells to me really cheap. They get puled pork and/or ribs out of the deal.
Hope this helps and I hope you enjoyed your meal.