Updated June 5th, 2019.
Apple has modified its return policy for the holidays:
“Items purchased at the Apple Online Store that are received between November 14, 2018 and December 25, 2018, may be returned through January 8, 2019.”
This should make it easier for people giving (and receiving!) Apple products as gifts, as Apple’s standard return window is limited to 14 calendar days.
Here is a link to Apple’s Returns & Refunds web page, a useful read as there are some “terms and conditions.” Note that only items purchased directly from Apple, either online or at an Apple Retail Store, are eligible for being returned to Apple. Resellers such as Amazon (referral link) have their own return policies.