When choosing a program like this, it's important to remember to not only choose two pieces from different eras but also two pieces that have different types of technical challenges and general sound. The first rule in choosing repertoire in a program is DON'T BORE THE JUDGES. Also I'd have to say that's it's probably a bad idea to perform anything that is too obscure in such a short program. If it were longer you'd have been able to mix some underplayed stuff with common repertoire but I suggest you stay in the realm of things the jury will be easy to judge your performance on. If I were you I would probably use either a shorter Mozart Sonata (IE K. 280) or Haydn Sonata (Hob:XVI32) or an early romantic piece like a movement from a Beethoven Sonata or a Schubert Impromptu, followed by something in the late romantic or possibly even modern era like a Debussy Etude/Prelude, Liszt Etude (Maybe Un Sospiro or Wauldesrauchen), Rachmaninov Etude/Prelude, Scriabin Etude/Prelude/Mazurka, Shostakovich Prelude and Fugue or something along those lines.
Good luck and have fun ^^