Welcome aboard Iconnolly. Congratulations on choosing the WSM.
I personally like cooking Baby backs low and slow, (Without foiling during the smoke), and I pay particular attention to smoker temps keeping them as close to 225* as possible.
I don't pay too much attention to passing time but after 5 hours will start prodding the ribs with a toothpick or similar thin probe for tenderness. This test for tenderness is a learned feel and so I suggest you start testing after about 4 hours of smoking and you will be able to discern the advancing "feel" of the probe as the ribs get tender and "done".
A good thermometer will be a big help in keeping tabs on the smoker temps,
(Don't bother trying to track rib meat temp, too hard to get an accurate reading, too many bones too close together. Can't get an accurate temp reading). Ribs are rolled and scewered to localize them in the "sweet spot" on the grate for temp.
This smoke was obviously done on a kettle and not a WSM. The same smoke on a WSM will be a good bit easier. (Easier temp controls).
Shop for the meatiest, (Thickest), rack of BB's you can find and keep those smoker temps low. Patience, Grasshopper!
Edited by One eyed Jack - 2/18/15 at 8:17pm