I'm wondering how in the world they even know about time compression, considering time travel doesn't really exist up to that point in time. Perhaps the spell exists in some form and they're aware of its existence even though it can't really be used. But then again, why would it even exist at all if no one could use it, and how would they know it would work?
I always assumed it was Edea saying this stuff and that she kept some of Ultimecia's knowledge from being possessed by her. That makes some sense, right?
--
http://s3-ec.buzzfed.com/static/enhanced/web04/2011/12/4/12/enhanced-buzz-wide-5065-1323019200-17.jpg