Granted that the secular interpretation of "apocalypse" is terribly vague, and not even limited to "mystical conflicts" - sometimes it just means an unspecified Bad Thing that turned Max Mad and filled the blasted deserts with giant mutant scorpions. But still, when one is actually telling a story about demons and devils and hell and the prophesied final showdown between the forces of good and evil, I think you're going to have a harder time invoking secular usage as a defense. :-)