My incubator was off for between 12 and 24 hours (lead accidentally pulled out)with night time temps. in the 40s, and hatched 5/6 eggs successfully. I was only on day 7, though. Fingers crossed and you may still have a good hatch.
If the temp. goes too high and for too long then the embryo will die, but if the temp is too low and not for too long, the hatch is delayed, but still usually is successful. Nature has a way of compensating for hens who go on holiday during their brooding, get lost going back to their eggs, or lose a few for a while at the side of the nest, but not generally for unintentional attempts to cook them. If the temperature spike is short you may, however, still get away with it.