From what I can tell, the only nontrivial difference between Nigerian Standard English and the catalog of commonly referenced dialects of English is that Nigerian Standard English has a different prosody, as it is syllable-timed as opposed to stress-timed.
I'm having a difficult time finding examples of dialects of a language with differing prosodic qualities. Given this, is Nigerian Standard English categorized as a discrete language, a dialect of English, or does it fall under some other category?