I put them on when I assemble the cooker and the smoke till nicely colored. I don't really cook by time but this usually comes in at around 90 minutes. If i am foiling I then foil with a little juice reduction and cook till tender while in the foil. This is usually 40-45 minutes but I have had them hit tender in as little as 30, or as much as 50-55. It depends on how long they cooked before foiling.
Since the ribs are now done, only a few minutes are needed unfoiled, to firm the surface texture.