FedEx seems to be limiting employee travel and training around this period, making sure as many workers as possible are on hand to deal with the surge of shipments. The carrier is generally Apple's primary shipping partner for U.S. orders, although Apple will sometimes use other carriers such as UPS during times of heavy demand.
The site obtained a note that reads:
"Due to the upcoming 'surge volume' event between Sep 21-24, this class has been postponed to the week of Nov 5-9 and you have automatically been moved to that class. If you are unable to attend the week of Nov 5-9, please send me an email and we'll remove you from the roster."
Notably, both AT&T and Verizon's vacation blackout dates are also said to begin on September 21st.