Why is the phrase “dark of the moon” wrong to you? It is a perfectly (well, all right, maybe imperfectly) proper English phrase with a history dating back to at least the 16th century (as per the OED).
The title reference is clearly to the dark side of the moon, as the opening act makes clear. That said, while the phrase “dark of the moon” is irrelevant to the movie, it’s true that the subtitle would not have assaulted my ears as it did had I been familiar with its prior usage. It just would have made me shake my head at the stupidity of its misuse. One of the great things about this job is that there’s always an opportunity to learn something, even with a review of a brain-dead movie like this one. Thanks for writing.