It will depend on the smoker, and the style of wood(chips,chunks, logs). If you are using chips in an electric smoker I have read about every 45 mins or so. If you are using chunks in a charcoal and cut the wood to about the size of a briquette and mix it in good using the minion method never! As to whether or not the meat stops absorbing smoke, that is one of those ongoing debates. Most people on here who smoke the entire time the meat is in the smoker, will tell you that it will absorb smoke as long as you make smoke. So be careful with the hickory as it is a bit strong, unless you like it strong!!