It takes around 6 hours to fully smoke a stack of ribs in a smoker.
When smoking ribs you should set the smoker at 225 F and then every hour while the ribs are smoking you can spray the ribs with some beer, water, apple juice etc.
Spray the apple juice, water, beer or whatever you want to spray on the ribs every hour while the ribs are being smoked.
The ribs should be ready after 6 hours of smoking them at 225 F.