Question
When there are back to back holy days and Sunday, when does the solemnity or feast begin and which Evening Prayer, I or II, do I use?
--Eager in Engelton
Answer
In Eucharisticum mysterium, written in 1974 by the Congregation for Divine Worship, a rule for the Saturday night Mass follow the rules for Saturday night Evening Prayer. In the General Norms for the Liturgical Year & Calendar [GNLYC], 61 it says:
Evening prayer of the day with the higher rank. . . takes precedence; in cases of equal rank, evening prayer of the actual day takes precedence.
GNLYC 11 talks of how solemnities are celebrated in the evening of the preceding day. A solemnity is either a Sunday (because it's the Lord's Day) or a day like the Assumption of the Blessed Virgin Mary. This follows the Jewish demarcation of time, which believes that the day ends with the sun setting and a new one begins. As an example, let us say that the Immaculate Conception is on Saturday, December 8. The Evening Prayer I is celebrated on Friday night, December 7. Evening Prayer II is not celebrated the evening of December 8. Instead, Evening Prayer I for the Second Sunday of Advent takes precedence.