They're pretty resilient to temp drops. You have at least an hour at that age, and probably longer. This year I have twice rescued eggs from a broody's nest after she's gotten up and abandoned them for who knows how long, put them in the incubator, and they still hatched. One was without heat for at least 24 hours. However, it was pretty far along.
I would, just in case, add heat sinks to your incubator which will keep the temperature up longer should you lose power. Things such as a bottle of water or river rocks act as good heat sinks.
Also, if you have hand warmers, like you would use in your gloves in the winter, those can be helpful. They generate heat when activated, so adding them to the incubator can actually keep the temperature up if you put in enough of them. I used them once when we had a long power outage in January and it kept the incubator warm enough that my eggs made it.