For my current pieces it typically takes anywhere from two to three weeks. I'm not sure how many total hours I usually spend on them during that span. Probably somewhere around ten, though I don't keep track at all, so there's a huge margin of error on that.
I understand, but we get better and better in the end. Take like one week for me to make a comic page, for color it with digital programs thought. A comic scetch can take a day or two dipending on how clear my maind is on the pictures.