In the Byzantine tradition, Holy Saturday beings with the Orthros (Matins) on the evening of Great Friday. This is the day between the crucifixion and the resurrection . On this day, Byzantine spirituality reflects on Jesus' descent into Hades, the dwelling place of the dead.
The Liturgy of St. Basil, celebrated on this day, reminds us that Jesus descended into Hades to loosen the bond of death. Death has no power, it has been defeated from within, by the power of Christ. This is the longest liturgy of the liturgical year.
In the Byzantine Catholic tradition, Holy Saturday is a day of vigilant anticipation. On this day, the liturgy focuses on Jesus' rest in the tomb. Jesus observes the Great Sabbath, but his rest is not inert, mourning is radically being transformed into joy. Jesus' tomb is not an ordinary grave. It is not a place of corruption, decay and defeat. It is life-giving, a source of power, victory and liberation.
Later, just before midnight, Pascha is celebrated beginning with the Midnight office, the first part of the paschal vigil in the Byzantine tradition.