The Enchiridion Indulgentiarum 26 indicates that we can gain plenary indulgences on 31 December and 1 January.
§ 1. A plenary indulgence is granted to the Christian faithful who, in a church or in an oratory, are present [take part] in a recitation or solemn chant of: …
1° the hymn Veni Creator … on the first day of the year, imploring divine assistance for the whole of the coming year…
2° the Te Deum hymn, on the last day of the year, in thanksgiving to God for the favors received in the course of the entire year.
