My theory on the plot so far.

What if the Black Mage's objective is to absorb the Goddess of Time into himself, thus allowing him to become the God of Time and by default the world? If the Goddess of Time is powerful enough to create or destroy the world...the Black Mage would then be able to control the world as he wishes, perhaps even create a new world after destroying the current one...a new world where he reigns supreme.