How to create a scheduler for updating a boolean value using Rules?
It's defined in node.module like follows

define('NODE_NEW_LIMIT', REQUEST_TIME - 30 * 24 * 60 * 60);


AFAIK, you can't redefine this value. I think you need to change and use your value in all the places.

I'll check and If I found better option I'll update my answer :)