What I do is take the filter material out and set it in a tuperware container and put a battery operated air pump underneath the filter material. Then float the tupperware container in the tank. I've left it in their for 34 hours once when my power went out durning a thunder storm once and I had no ill effects.
My tanks been without power for about 8hrs on one occasion, power went out over night, I didn't know until the morning, everything was fine. I wouldn't worry too much.