The night before Christmas Eve is "Christmas Adam".
"Christmas Adam is a colloquialism for the day before Christmas Eve or December 23rd. It is a rather new term. An online slang dictionary created a listing for it in the early 2000's. Christmas Adam is not listed in any formal dictionaries.

The general consensus of the origin of the name is that in anticipation for Christmas to come, people were looking for a name for the day before Christmas Eve. Some were calling the 23rd Christmas Eve Eve. Then someone (or more likely several someones) realized that in Christian mythology God created Adam before he created Eve, so the day before Christmas Eve would be Christmas Adam." grammarist.com

Each year, it catches on in more and more places: https://www.nytimes.com/2024/12/22/us/christmas-adam-dec-23.html

Christmas Adam is primarily celebrated in the United States. It's not a widely recognized holiday, in fact, it's more of a fun tradition or a playful way to add an extra day to the Christmas festivities. Individuals and families who enjoy extending the holiday season often observe it by engaging in cozy, relaxed, and festive activities.

At our house, we celebrate Christmas Adam, Christmas Eve, and Christmas Day. We like Christmas!!!