How long do fowl eggs last if incubator fails during incubation?

My incubators both lost power supply today after a trip switch tripped, the temperature had dropped to 23 degrees C before I noticed. I am quite upset as I had nearly 100 eggs that had been incubated for 8 days when it happened. Will the embrios be OK? What temperatures can they drop to before failing? Thanks in advance for any sensible answers.