Rather than delay cleaning, I would suggest doing it one day early. The main question may be if the outage should last longer than planned. IT happens, soo being prepped is good. So if the bacteria may be knocked down a bit, having the filter clean, gives them less to do but that cleaning should be done to avoid killing too much of the bacteria on the media. Since the tank is new, the bacteria will just be getting settled in on all the other parts of the tank, so clean gently, just to reduce the big stuff. No hot water nor chlorine, for sure!! Do NOT wipe down walls, etc. as we might want to call any of that slick stuff bacteria until we get sure of there being plenty.
During the power outage, there may be some value in having a jug or two of water on hand. Treated and at near the right temp, the water poured through the filter will be worth it---if practical.
But overall, this is not a major bump and may not create much trouble. Staying alert that it might turn bad is one of the better ways to avoid the gremlins! Testing or watching for fish acting a bit "off" is always good at these times. The time is not too serious but pouring water is one way to get by, even if we had no filter. It's just more work than most of us can handle for full time!