AHHHH this question
This all depends on the skill set of the blower. A newbie will take maybe 15 and the pipe will look like crap. A good blower can wing one out in 8 and look amazing. Now this also depends on how thick the glass is as thinner is way faster.
When you look at glass its not how long it took to make it for that piece. But when Steve makes a piece it took him 15 years to do it.