time-sensitive

A question I am occasionally asked: "How long did it take you to do that painting/drawing?" or the more general, "How long does it take you to do something like that?" I've observed that this is never posed by another artist, but a person who does something else altogether for a living. Unless it's another artist asking specifically about a technique or material that we both use, which is more like shop talk.
As with other questions in the same vein, the patience of my reply depends on their tone and delivery. I can never come up with a simple answer. I'm guessing hardly anyone could. I might work on several pieces at once, or have to do other things that interrupt or slow my progress. Certainly there are some pictures that I sit down and work on for six hours straight, making it possible to calculate. However, making a work is not just when the brush hits the paper/canvas, but everything that comes before- initially finding, seeing (or imagining) the subject, then working out the composition and so forth. I might stare at a drawing or photo for years before using it, or rework something over months.
I wonder what printmakers and photographers say- making a print could take only an hour, but the preparation takes days or weeks. Or my friend who makes ceramics- she throws a kiln-load of pots at a time, dries & fires them, meticulously glazes and fires again- how does she say how long a piece takes? It can open up an absorbing discussion, but doesn't exactly lend itself to an easy reply.
Yet, when pricing art, we try to use this information to decide what we want or need to get for each hour of work- putting it into more conventional job terms.
The related question is, of course, "How do you figure out what to charge?" What is your time worth? The questions spiral. Did your time start when you were born? Your time in school, or working for someone in your field, and what about the time you spent in art-supply stores and in museums? Can you quantify it? I know some artists do. I try, to an extent. Wait, but if I loved doing it, was it really 'work', or a so-called labor of love, so how do you price that out? I don't mind the curious & pleasantly-posed questions, as long as people don't mind the long musings. I can also offer a brief  "Ummm... ten or twenty hours?" my voice rising at the end, as if it's anybody's guess.