This Sunday both concludes Christmastide and begins Ordinary Time. Is that safe to say? I would suggest that, in fact, it is the first solemnity of Ordinary Time because it inaugurates the First Week in Ordinary Time. So a case can be made that it isn't the Christmas Season at all and all decorations should be removed for this Solemnity in Ordinary Time.
But a case can be made that this Solemnity continues the Solemnity of the Epiphany becasue the baptism of Jesus is a theophany or manifestation of God particularly in God's voice being heard to say that "this is my beloved son."
Perhaps it is just a continuation of the Epiphany Season. But is it? Yes and No, not either/or but both/and.