You can enjoy the Neapolitan Christmas from December 8 till January 6. These days are traditionally considered as the beginning and the end of the Christmas season.
December 8 is the Festa dell'Immacolata Concezione (holiday, the feast of the Immaculate Conception). Traditionally the Neapolitan begin the building of the crib.
On 6 January is the Epifania (Epiphany holiday, in informal talk called Befana too) and is the last holiday of the Christmas season: cribs, Christmas tree and Christmas lights are removed.