Not well known?
Sorabji - Etudes Nos. 26, 36 and 59
Alkan - Op. 39 No. 12
Elliott Carter - "Two Diversions" (more than one movement, but what the hell)
Boulez - Sonata No. 1 (same as above)
Godowsky - tons of transcriptions to choose from, though I'm not sure how long some of them are
John White - some of his piano sonatas may have the length you're looking for
Medtner - lots of miniatures to choose from (I really like his Op. 10 No. 2, for instance), and if you're as good as Hamelin

, you could play his Op. 30 in 12 minutes; if you're looking for variations, then you might want to check out his Op. 55
Messiaen - pretty close to "standard repertoire", but anyway, his
Vingt Regards Nos. 6 & 10 are both safe bets
Sorry for suggesting so much 20th-century music.
