Mass is offered every day of the year except Good Friday and Holy Saturday, the vigil of Easter.
In the first centuries, bishops and priests celebrated Mass together; this is called concelebration. Our present Masses, when priests are ordained, and bishops are consecrated, are similar to those early Masses.
1. Ordinarily a priest is permitted to say mass only once a day. On Christmas and All Souls’ Day, however, he may say three Masses.
On Sundays, holydays, first Fridays, etc.., a priest with permission may say two, and even three, Masses when the people’s needs so require.
2. Mass is usually said in the morning; with the approval of the bishop, it may also be said in the afternoon and evening.
In the early days of Christianity Mass was said in the evening, after the example of the Last Supper, when the Mass was instituted. Later it was thought better to have it said in the morning, for a greater respect to the Holy Eucharist. In these our days, Mass may said at practically all hours of the day, in order to facilitate attendance and the receiving of Holy Communion.