What is saturday vigil mass

The Code of Canon Law (can. 1248) permits Catholics to fulfill their Sunday and other Mass obligations by participating in Mass “in the evening of the preceding day.”

Pope Pius XII, in the apostolic constitution Christus Dominus, set the earliest hour for such a Mass at 4 p.m.

Rule VI.

If the circumstance calls for it as necessary, We grant to the local Ordinaries the right to permit the celebration of Mass in the evening, as we said, but in such wise that the Mass shall not begin before four o’clock in the afternoon, on holy days of obligation still observed

Until the Church issues a new rule regarding when to officially define “evening” in canon 1248, 4 p.m.

remains the earliest time a Mass is considered to fulfill the next day’s obligation.