You can take years to answer the 500 questions.   When you answer any particular question you have to edit the question at the same time (within 12 hours of answering) for it to count towards the badge.

This is to prevent people from going back and mass editing lots of questions that they already answered just to get the badge.

The [illuminator badge was announced in September 2014](http://meta.stackexchange.com/questions/239898/new-three-tiered-badge-idea-explainer-%E2%86%92refiner-%E2%86%92-illuminator).  The thread in meta announcing it has a lot more info about the requirements for it and the rational for creating it.