The development of the embryo is driven by the temperature of the egg. If the temperature increases, the development will go faster and the chick will hatch earlier. However, increased temperatures have a risk of resulting in poor chick quality.

There are two climatic factors that mainly influence the hatch time. The time between the start of the incubation process and the optimum time for pulling-out the hatch.

- Start of the process.
The embryo will be developing at its optimum speed at an embryo temperature of approximately 100oF. As warming the eggs at the start of the process takes time, it will take the embryo several hours before it is developing at its optimum speed. This warming time depends on the type of machine, actual climatic settings as well as on the temperature of the eggs that are entering the machine (storage temperature and pre-warming).

- End of the process
During the last half of the incubation process, egg temperatures will rise above air temperatures due to the advancing development of the embryo. This will influence hatch time, as higher metabolic heat will increase embryo development.

Next to these factors, egg storage and age of the breeder flock can influence hatch time.

- Stored eggs need longer time to incubate. In general, every day of storage adds 1 hour to the incubation process.
- Eggs from breeders between 35 and 45 weeks of age hatch quickest. Eggs from older but also from younger flocks normally take longer incubation.

Although a standard incubation time depends on several variables, as a rule of thumb, the incubation process should take a minimum of 21 days and 4-6 hours, and an optimum of 21 days and 12 hours. If hatching occurs significantly quicker, chances is, the embryo temperatures are high and the chicks get overheated.