When did the WW1 Christmas truce end?
I would recommend a book called “Silent Night” about the Christmas truce of 1914. In some parts of the front, especially where Anglo Saxon Brits lined up against Saxon Germans the truce lasted for quite a while afterward…up to the new year sometimes, or until one division or another on either side was moved out and replaced in the line. Even after they were ordered to fire upon one another some units chose to warn their opposites that they were going to shoot or just fired into the air.