The big bowls of the 1990s (magnum, ODA, ODB), up to 2 hours. I have a couple now (group 6 or so) that when relaxed and smoking right (me, not the pipe), 60-75 minutes. But usually 20-30 minutes for a group 3-4. Sorry, but I grew up around Dunhill collectors (never one myself), and the sizes are set like concrete in my mind. Even though 20-30 is my norm now, I also know that it is too quickly. If all variables were in my favor, those same pipes would be more like 45-60 minutes. I feel pipe smoking is a slow deal, but the times ain't.