The Saturday Evening Service is called Great Vespers. It lasts about an hour. Orthodox Christians, like the Jews before them, believe the new day starts on the evening before. Great Vespers is a preparation for, not a substitute for, worship at the Sunday Liturgy.
It consists mainly of singing of Psalms, especially Psalms 104 and 141, the “evening offering of incense, and the hymns “O Gladsome Light …” and “Now dost Thou dismiss Thy servant …” (Luke 2:29). The service has themes of Creation and Resurrection as the “eve” of the Day of Resurrection, the first day of the week.
Vespers is also served on Wednesday evenings in our parish. This follows our daily structure of prayer which starts with Vespers. Then Compline, First Hour, Matins, Third Hour, Sixth Hour, Divine Liturgy and Ninth hour complete the daily cycle.