If you have a power failure for sure do not open the bator as it can't recover. Power failures of up to 24 hours may only delay your hatch if you leave the humidity intact in the bator and keep it away from drafts so close the door to that room even. Do not however block the air from circulating into the bator via the vents, the eggs still need to exchange air, so wrapping the incubator in extra insulation is not a good idea.
Towards the end of incubation the developed chick can create some heat it's self so you may not even see a delay in your hatch date. Them hatching out in the power outage would be more of a problem due to them being chilled by being wet.