I've never gone over 2 hours with a canister filter. They go bad quicker because they are a closed system. As far as HOB's I'm not sure, when I've had a piower outage I've used battery operated airstones on the filters to keep some circulation going
When the room temp is around 68* or lower and tank is kept at 76*-78*, I would think, imao, that 'good' bacteria would die quicker than 12 hours. On the instructions for the water filters I use, they say you can gently rinse off the filter, using treated water that is close as possible to tank temp, otherwise you could possibly kill off the useful/good bacteria that's on the filter/media.