Hatching time frame question please advise

[kitten4686]

Picture taken 9/7
Hen not sitting yet

Picture taken 9/13
Hen not sitting yet

Picture taken 9/14
Hen is now sitting
HELP QUESTION IS WHEN WILL THEY HATCH?
Do I go from the time 1st group laid (9/6) or rest laid between 9/7 - 9/13 or do I go by sitting date? If I go by 3weeks from laid first dates they should already be hatching.... please advise:/

 

[1cock2hens]

Sitting date, the he chicks don't start developing until they are at a certain temperature for a certain amount of time (numbers aren't my strong point) sorry I can't be more exact with my answer. Im sure someone will elaborate