I believe there's a 60-second limit - Megacon's anime costume contest is focused on craftsmanship, not performance. There is also the Universal contest, but I think that too is craftsmanship based.
2014 - Upcoming Conventions :
Holiday Matsuri (FL)
Upcoming costumes : Suzie Q from JoJo's Bizarre Adventure, Edea Lee (various versions) from Bravely Default, Robotnik (genderbend) from Sonic, and more!