When did Saturday night Mass for Sunday start to be allowed?
First, please remember that Judaism in Jesus’ day considered that a “day” began with sunset of the previous day. Jewish feasts still follow that custom. Although some Christians accepted this calculation for their own celebrations, most people considered a “day” to go from midnight to midnight.
There were already late afternoon and evening Masses before Vatican Council II (1962–65). Until 1953, however, Catholics were normally expected to fast from everything (water included) from midnight before receiving Communion. In the decree entitled “Christus Dominus,” Pope Pius XII granted local bishops permission to allow late afternoon or evening Mass before a Sunday, holy day of obligation, or other major feast—as long as the Mass did not begin before 4 p.m. I have a very clear memory of participating in a parish Mass for the feast of Mary’s assumption on a late afternoon one August 14. This was sometime before 1962.
In 1953, the eucharistic fast was changed to no solid food or alcoholic drinks for three hours before Communion. Other liquids could be taken up to one hour before Communion.
On May 25, 1967, St. Paul VI approved “Eucharisticum Mysterium,” which made late afternoon or evening Masses more common. Pastors were instructed to explain that the biblical concept of “day” extended from sunset to sunset; later Saturday afternoon was already “Sunday.” The eucharistic fast was changed to one hour before receiving Communion, with no restriction on when medicine could be taken.
As happens with some frequency in the Catholic Church, a liturgical practice already permitted for a particular region can later be extended to the whole Church.