Juli Clover, MacRumors:

Items purchased from the Apple Online Store that are received between November 10 and December 25, 2020 can be returned to Apple until January 8, 2021, offering holiday shoppers more than two weeks to make returns.

These dates are applicable for the U.S. store, but Apple also extends return periods in other countries as well.

That’s an amazingly generous return window. You can buy a new M1 Mac today and have almost two months to return it.