You can go to 11/13 (11 hours lights on, 13 hours lights off) to accelerate maturation, but any less than 11 hours of light will not be enough light for a correctly functioning metabolism and will delay maturation considerably.
11/13 is a good schedule to use when it comes to finishing flowering with Sativas, as it slows the plant from constant re-flowering and negates its stubbornness to finish maturing.
Hope this helps, Organoman.