The period from 27 to 31 December is fully part of the Christmas season, namely the 3rd to the 7th days of the twelve. Traditionally the festivities lasted all the way to Twelfth Night - but on no account would decorations etc have been put up before Christmas Eve.
I was once told by a Spanish colleague that it is not done in Spanish-speaking countries to wish someone a Happy Easter before the day itself (even if you are not going to see them again until after Easter), as that would be to disregard the significance of Holy Week and Good Friday.