As long as you don't have an open container of high octane beverage nearby, and your furniture and rugs are fire retarding, you may be o.k. But not recommended!
Is someone going to graph these replies??
If I had to choose, I would say right after I wake up. A pipe and coffee is my favorite way to wake up. That's what I'm doing right now. But in all reality, I enjoy it all day long.
Late evening on the weekends, as the sun starts to set and everything is peaceful, no better feeling than reading a good book, smoking your pipe and enjoying that peaceful moment!
Also I find that Christmas Day afternoon pipe is next to none too...
My absolute favorite time is a crisp evening outside next to a campfire, preferably in the middle of nowhere. Following that, late at night during astronomy. Last but not least, the evening, after work and dinner.