If I ace the sketching layer I'll just make it the inking layer. When I do that, the comic only takes a measly 4 hours. Usually, though, it takes closer to 5 or 7. If it's a rough comic, like the one I'm doing now, it can take 10. And that's faster than I used to do it, too. Once I settle down with the art style it'll hopefully go a lot faster.
I usually break my comic down into 2-3 hour sessions every day 6 days a week. That leaves one day for video games or other projects or catch-up for when I can't get my comic done between 4 hours of school and 8 hours of work.