EssaySnark recommends, *do not quit your job yet.* It is easier to get into bschool while you're employed. If you have another job lined up, fine -- or if you want to go get another job, that would be OK. But you will need to be able to talk about how that new job is preparing you for your future goals. And, some might say that it's unethical to start a new gig if you know you'll be leaving in a short time. (EssaySnark is on the fence about that one.) You have a year before you'd start at bschool, and it's important that you FILL THIS TIME WISELY.
EssaySnark has seen people quit their job because they assume they'll get into bschool, and not only can this be perceived as presumptuous (even arrogant) by the adcom, but it puts you at risk for ending up next year without school and without a job. It doesn't make you look like a good planner.
If you quit now, you just need to come up with a good reason for why, and you'll need to find challenging projects that are giving you skills to enhance your profile.
It's not technically necessary to have a job while you go through the admissions process. But you'll be asked about your employment situation during the interview process, and you don't want to sound flaky. Also, we assume that you'll need to get letters of rec from your current employer, and those will likely be easier to obtain if you're actually still working there.

Maybe you can talk to your manager and find more exciting projects, or come up with your own initiatives to propose? That would make for good essay material potentially too.
And yes, you could be a good candidate for Duke Early Action, provided you're 100% committed to that school. Cornell and McCombs haven't released their deadlines/rounds yet we don't think, but in the past they've had "early action" rounds too -- and you would only want to do one school's "early" program. You can apply to multiple R1 schools, but just one so-called "early" round (EssaySnark has an article on this queued up for early next week, check our blog then).
Good luck with it!