also depends on the circumstances. if the artist is really busy with other commissions then you have to be somewhat patient. I have been waiting 3 months for a painting from one of our DA guys but i also know he is very busy.

A few days!! Unless occupied with other commissions/ priority work!

I think it depends on the complication of the image as well as the medium used.

For me, I work only in with original art sales and traditional media so it tends to take a bit longer than digital pieces depending if it's BW or color. None the less, that all depends on what the client is paying as well. But if there is a deadline set the artist can either agree or deny the commission. Personally I always like clients to be patient so the image can be produced the best for the client as well as the artist's interests.

A few days.