ok so the only concern that i have when you turn on the fan 24/7 your temp spikes. Well this makes me think that maybe you have temp variation and when you turn on the fan it is evenly dispersing the heat. And also i would recommend getting a thermostat like a herp stat that is not a on off type so when you set it to 89 it holds it at that temp. Thats just me personally. I mean you are taking all this time to raise and breed for these eggs. Why risk anything going wrong while your incubating. Replacing your thermostat like a herp stat should help you. Having the fan is key to circulating the air. If it turns on every 40 min then since heat rises then in that 40 min that the fans no on all the warm air is staying at the top of your incubator. Hope this helps a little