I would expect the email notice on the hatch day itself.My understanding is that the dates listed are hatch dates, so I would assume any sort of shipping notice would come by the next day, giving them time to pack and make any substitutes due to hatch results.
The chicks MUST be shipped before they are 24 hours old, because the Post Office insists. They can only go so long without eating & drinking, so they have to be shipped fast.
Ideal Poultry somehow manages to ship them even before the hatch date: I've had several orders from them with a Wednesday hatch date, but I got an email with a tracking number on Tuesday evening.