I think this stems from a university study from a few years ago. They determined that slightly lower incubation temps favor females, and slightly higher temps favored males. But this was a very slight difference, I think maybe 1/2-1 degree? And this only very slightly shifted hatch rates in favor of one over the other. There is no way to change the sex of an egg after fertilization. I have had hatches in January from very cold eggs run at 80% male, and vice versa. I actually run my Brinsea at a slightly higher temp (100.4), because I find I have better hatch rates that way, and it seems to have no effect on sex ratio.
There is one theory I do subscribe to regarding sex rates. There was a study that showed that early eggs in a hen's life are more likely to hatch male, and I really think I've seen evidence of this with my hatches. My young hens usually start laying their first eggs right after the new year. I always end up with more males out of those early hatches, as well as from younger hens, than I do from older hens or late spring/summer hatches. So I try to avoid setting eggs from my hens until they've been laying for a few months.
As far as power outages and turned off incubators, hatching eggs are surprisingly resilient. It takes quite a while for the interior temp to drop dramatically. Broody hens leave their eggs unattended for an hour in very cold weather. Once, I had some unhatched eggs on day 23 of an incubation that I assumed was finished. I candled the remainders, saw no evidence of life, and sat them on the counter to be disposed of later. 8 hours later, I heard chirping from one of the eggs! It had internally pipped! I quickly returned it to the incubator, and it hatched a perfectly healthy chick. I couldn't believe it! That chick was like a miracle.
(I only check a couple of them, but jeepers it's hard to wait!)
