It means turning over every 90 minutes. Although the incubator can be set to turn eggs automatically every few hours, it should still be turned manually every day or two. This is to prevent the growing embryo from sticking to the egg membrane and dying ... egg cooling: you don't need to cool the egg for the first 7 days. After 7 days, the temperature in the incubator is unstable due to the increased heat production of the embryo itself, so you should cool the eggs once a day in the middle and late stages for about 15 minutes.