And the problem is, there's no good (easy, accurate, satisfying) answer to this question.
This is the current state of my drawing table. These are all study drawings, done with white charcoal on black paper, created in the last few weeks to test scratchboard ideas for SEWE. (This isn't even all of them! there are at least half a dozen more not shown). Of the pile o' pictures here, only two have become scratchboards. Most of the rest will not go any further, because I don't think them worthy of becoming finished artwork.
How much time was spent creating these drawings? There's no good answer to that, either - because each drawing represents uncounted time that was spent looking at and fiddling with my reference material, as well as turning ideas over in my head, before actually putting pencil to paper. (It's worth noting that the relative speed with which I create a drawing is due to decades of drawing practice, which adds yet another variable to this unwieldy equation.)
Once I decide an idea IS worthy of scratchboard, there's finicky prepwork involved with transferring the image to the board, so I can avoid scratching in the wrong spot (leading me to destroy the board and then commit hari-kari with my xacto knife. Not pretty.)
The amount of time spent on working a given board then depends heavily on factors like the size of the board, the amount of black in the image, how much coffee I've had, etc.
And note that this is all specific just to scratchboard. There are different processes involved with creating an oil painting, involving both sketches and Photoshop work to help me visualize the final image.
SO, how can I answer the question "how long did this piece take?" in a way that is both accurate and satisfying to the questioner?
I'm open to suggestion! Readers, fire away!