For me it really depends on the style I am using! A sketch for me only take about 5-10 minutes digitally and traditionally up to 3-7 minutes. I apply fast and quick strokes and scribbles that sometime do not make sense, and to ink in a piece that I may like takes up a half-hour or more depending on the complexity. For digitally, it takes longer because I am still not use to the pressure with my Tablet. Traditionally, it is also a bit of a challenge because of my new manga inking pens having a different feel and use than my Sakura pigments; it's a pen nib that you must dip in ink and let sit to dry. Colouring really varies. But sadly, I am a very lazy artist as well because I don't like to finish all my pieces or some are destined to be in the abyss that is my computer. XD
For cel-shading, defined as two-three shades and highlight, it takes about 45 min-2 hours of my time to make a fullbody markup like
this.
CG Painting, if my time is openly spaced, would take me 2-4 hours, but if the piece may have shoddy edges, it means that it took me at least 3 hours. The more smoother and defined it is, means I took two days and total of 6 hours. XD Something like
this is what I call extra release of artistic pressure, something that I wanted to just experiment with for fun, took at least half an hour or so. I virtually use up to 3 layers for sketching, and sometimes I go right into colouring right after sketching in one layer.
Manga is the devil for me; it racks up to 4 hours per page- including sketching, inking, white-out, then scanning for extra original copy before being toned. I can never apply the right computones I want for an image, nor can I ever keep consistency with the toning because I have too many tones to use. @w@ I do not have any formidable samples to show of my manga because frankly, I haven't done it in a while. XD