I concur with everyone above.
There is no hard and fast rule about bowl duration.
Some things that can effect your smoking duration:
Tobacco Preparation,
Packing,
Good Char and True light?
Puffing technique,
Tamping technique,
Size of the bowl,
Choice of tobacco,
Choice of pipe,
Is it raining, drought?
Hot or cold?
Windy or calm?
Fish biting or not?
Mad or glad?
Reading, watching a movie, listening to music, playing poker, party or thinkin' drinkin'?
Is the traffic good or bad?
Lots of variables can affect duration, and I might add enjoyment.