Starting with 17 merits awarded to some of my old Jr. Member posts by people who remember them, I reached the Hero threshold of 500 merits within 27 days, 8 hours, 16 minutes, 22 seconds of active posting.
But you will be the glaring exception here. In fact, you're probably one in ten thousand or something. I can't really think of another user here who made such an impact in such a short time and for users like you the merit system will work as intended. Great posters will have no issue issue in rising through the ranks so I don't think it should be made more difficult, though the numbers could be adjusted slightly I guess but we'll have to see how things go. Poor posters will get nowhere unless they abuse the merit system but I do have some sympathy with average or even 'good' posters as they could take quite some time to get the merit points they need or deserve. It takes 4.5 months to become a Full Member and nearly one and a half years to become a Hero so lets see how people get on over time because it's certainly too early to say right now.