Having smoked a lot of different meats / cuts, I can usually call it quits when the internal temperature hits my goal.

Pork ribs seem to be the exception. I can hit an internal temperature quoted on recipes for ribs and still be an hour and a half short of "tender". I usually ignore internal temperature on pork ribs and just start getting touchy-feely after about 3 1/2 to 4 hours at 250 to 225 degrees.

Exactly the same with me ~ ribs are tricky for me, but I usually go about 4 hours, no more than 5 (this is for spare ribs; baby backs will be probably an hour less).