An Epiphany A Long Time in the Making

I'm a native speaker. There is this sentence "an epiphany a long time in the making." Now it's technically an incorrect use of the word "epiphany," which is essentially something sudden. But what kind of mistake is it? What is the specific term for that kind of mistake? It's not a malapropism or a solecism. The closest thing is a "yogi berism" (No one goes there nowadays, it's too crowded). It's a phrase that's inherently contradictory. My question is, is there a name for this? I don't think it qualifies as an antithesis. Any linguists out there who could help?

Solution 1:

What you’re describing is an oxymoron.

oxymoron noun A figure of speech in which apparently contradictory terms appear in conjunction (e.g. faith unfaithful kept him falsely true). - ODO

As others have cited, there isn’t necessarily a contradiction between a sudden realisation and an extended prelude to that realisation.