Sounds pretty close. I’ve heard that on average, smokers live 8-10 years shorter than non-smokers. So, in doing the math:
Let’s say someone started at 15, and smoked for 50 years, which is about 10 years less than “normal” average life expectancy.
50 years * 365.25 days * 30 cigarettes per day (pack and a half–don’t know what is “average” consumption anymore) = 73 = 547,875 cigarettes in a lifetime.
10 years is approximately 5,259,600 minutes.
Dividing 547,875 into 5,259,600 = 9.6 minutes per cigarette.
You can fiddle with the numbers a little bit, and probably end up with something closer to 5½ minutes, though.