Usually that isn't a problem. It does somewhat depend on the type filter you have though. The main thing is that the filter media stay wet. If you have an internal or external filter they will be fine. A HOB filter with filter cartridges should too. The ones that have the most chance of having issues are the bio-wheels where most of the bacteria populates the wheel which is out of water and can start drying out rather quickly. If that is the type filter you have, you can do a couple things so keep it in good shape. You can pour water into the filter every so often which will force water out over the wheel or you can simply remove the wheel and drop it in the tank to tay wet. When the power comes back on, simply reinstall the wheel and your good to go.
It takes quite a while before you really start losing a significant amount of bacteria. I have, on a couple occasions, forgotten to plug my filters back in after a water change and not noticed it for as long as about 20 hours and had no problems with a loss of bacteria.