It all depends on mood for me. My mood determines the length of time. If I am in an aggravated or intense mood, I can finish a bowl in 15 minutes easily. Calmer, tranquil moods can extend to a hour or so. As long as it is enjoyable or helpful, time is relative.
Slow to you preference. It's your pipe. You smoke it however you want to. Some like it so slow, pipe is between going out and coming back due to slow draw. I like it on a bit of warm side. Cold smoke taste like a dead gold fish that got stuck in a garden hose back from my elementary school. I had to drain a sink in 4th grade. Some memories just doesn't fade away.