It is an old tradition that Sunday begins at sundown.
Then why does the Conciliar sect have Saturday afternoon Masses that begin well before sundown and claim that these actually fulfill the Sunday obligation to attend Mass.
I am absolutely shocked at the stupidity of many of the answers on this topic. No Mass celebrated on Saturday fulfills the Sunday obligation to attend Mass. Even the Easter Vigil Mass (pre-Holy Week changes) didn't do this. This Mass was celebrated Saturday morning but the faithful who attended it were still obligated to attend Mass on Easter Sunday. The Easter Vigil ceremonies after the Holy Week changes are to be scheduled so that the actual beginning of the Mass begins as close to midnight as possible.
The Saturday anticipation Mass is a
novelty. It was invented by the Conciliar sect to diminish the people's obedience to the Third Commandment and has led many souls to hell.
Attendance at a Saturday Mass can never fulfill a Sunday obligation. If a person is prevented from attending a Sunday Mass due to circuмstances beyond his control, he does not sin as the Church
never commands the faithful to do what they cannot do. In such circuмstances, it may be laudable to attend a Saturday Mass (and, of course, I am not talking about attendance of any Novus Ordo Protestant Service) if one cannot attend Mass on Sunday, but this must never be considered obligatory nor as fulfillment of the Sunday obligation.