Hey there dude,
Sooo first of all, to answer your question about when to apply I need a lot more info from you. With 30 months already, you COULD apply this year, but I think you would have somewhat better chances next, so if you like your job and are doing interesting things, there's no reason for you not to hang in one more year and learn what you can, and strengthen your profile. Plus, at least on the surface working for your country's central bank is far better than big 4 experience, so you might want to spend time strengthening your profile there. It's entirely up to you of course, and this decision involves a lot of personal and professional considerations that are totally outside the scope of the MBA considerations...... but like I wrote, one more year feels good to me (it's also a great chance for you to boost what you can in your extras). But if you have a very good reason for applying this year, why not?
Second: CONGRATS on that super fantastic GMAT! That is really great! And it will help you a lot as you apply. If the other items in your profile are pretty good (like you have good ECs, good volunteer work, and can get good recs), I think that 740 + Central Bank + African applicant should allow you to apply to top 10 schools (and maybe two schools in top 20 as backups).
I mean it depends a bit more on what exactly you do, what your work experience looks like, etc. etc. but from where I stand things look pretty good, and if you can write fantastic essays, no reason why you should not aim for Tier 1 schools like Duke, Sloan, Darden, Yale... etc. etc.
Dropping out from your phd is no big deal I think. You will need to address this in your essays of course, and explain why.. but since you seem to have had a nice and successful career ever since you dropped out, it makes it seem like this was the right choice! It's all about what story you tell dude!
Sooo, hope all these thoughts help you get started out. If you have any questions, any at all, don't hesitate.
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