U.S. Apple Deadline
In the U.S., in-stock items ordered before 3 pm on December 23rd will arrive the next day in most metro areas. However, it is, of course, worth confirming your delivery date at check out.
UK Deadline is Sooner
For those in the UK, the final order date is 4.30 PM on December 22nd. Items ordered can be delivered or picked up from a nearby Apple Store.