Before laying:
Day 0-1:
The egg gets fertilized.
The cells split up into groups for specialized function.

After laying and incubations started:
Day 1:
19 hours: The gastrointestinal tract (Tube from mouth to bottom) appears.
19 hours: The brain crease begins to form.
21 hours: The brain and nervous system begin to form.
22 hours: The head begins to form.
23 hours: Blood pools form.

Day 2:
24 hours: The eyes and heart starts forming.
34 hours: The ears start developing.
41 hours: The heart begins to beat.

Day 3:
The head starts turning to the left.
The tongue begins to form.
The tail, wing and leg buds appear.
Internal organs(liver,lungs etc) start to appear.

Day 4:
The toes begin forming.
Their are changes in the gut.

Day 5:
The reproductive organs start forming.
The leg bones begin to form.
The crop (Food sack) begins to form.

Day 6:
The beak appears.
The wing develop elbows.
The ribs start developing.
The gizzard forms and intestines start looping.

Day 7:
Feather points grow on the tail and thighs
The knees develop.

Day 8:
The inner eye lid begins to form.
The egg tooth starts forming.
The bone marrow in the legs begins develop.

Day 9:
Upper eyelids develop.
knee caps start to form.

Day 10:
Claws start to form.
wing feathers appear white body feathers start to develop.
Lower eyelids develop.

Day 11:
claws begin to curve.
The beak starts hardening.
The embryo draws calcium from the eggshell.

Day 12:
Scales appear on the legs.
The ribs starts hardening.

Day 13:
The collar bones form the wishbone.

Day 14:
The embryo turns towards the round end of the egg.
The skull hardens.

Day 15:
The claws and beak become hard.

Day 16-17:
The beak turns towards the air sac.

Day 18-19:
The beak breaks through the air sac and the lungs start working.
The yolk sac begins to be consumed.

Day 20:
The embryo grows to fill the none air sac part of the egg.

Day 20-21:
The neck starts to spasm.
The egg tooth brakes the shell.

Day 20-23
The chick has hatched!