It starts on December 12th, when Santa Claus and Santa Claus 'messengers are seen in all cities and on December 31st, Santa Claus and Santa Claus' messengers disappear.
"Christmas is an event that was introduced with the 2006 Christmas Update. It starts on December 12th, when Santa Claus and Santa Claus Messengers are seen in all cities. On December 20, the Grynch Clan Goblins invade every city every day. The attacks last only 7 days until the Save Server on December 28. On December 31, Santa Claus and Santa Claus' messengers disappear."
Christmas | TibiaWiki | Fandom
"It starts on December 12th and ends on December 30th. When the event starts, Santa Claus will appear in all major cities in Tibia. When speaking gifts to him, the character will receive a random gift. Each character can only obtain one gift annually."
Evento de Natal - Tibia Wiki