Alright, to everyone who's worried about not getting their iPhone today:
Apple most likely told Fedex to override the system and write 6/24 as the delivery date no matter what because they expected to hold the packages for that date. For whatever reason, Apple decided NOT to hold packages after all. Upon making this decision, they had Fedex generate a list of all customers who would receive their package early, and then sent out emails to all of those people.
In other words, Apple wasn't guessing about the 23rd delivery date. If they said it will come today, it will come today. Fedex most likely just didn't update their system to reflect the new "real" delivery date, but rest assured, it will still physically arrive at your house/apt/office today.
FedEx's online tracking system is NOT REAL-TIME. They state right on their website that it's for informational purposes only, not to be taken as a definitive schedule. Sometimes I get packages DELIVERED before their system even says "out for delivery". It can be majorly out of sync with the real world at times. My advice? Sit back, relax, and wait till after 5pm before you start complaining. 😉