Dante's journey through Hell begins on Good Friday. The starting point of his journey is symbolically significant: Good Friday is the date on which Christians commemorate and celebrate the anniversary of Christ's crucifixion. Good Friday is the Friday before Easter (Easter always falls on a Sunday).
Through His death on the Cross, Christ redeemed the world from Sin. At His death, Christ descended into hell (temporarily) before His Resurrection on Easter Sunday. The Catechism of the Catholic Church states: "By the expression 'He descended into hell', the Apostles' Creed confesses that Jesus did really die and through his death for us conquered death and the devil 'who has the power of death' (Heb 2:14). In his human soul united to his divine person, the dead Christ went down to the realm of the dead. He opened heaven's gates for the just who had gone before him." (quoted in Wikipedia)
Dante's descent into Hell on Good Friday, his journey through the circles of the Inferno, and emergence from the other realms on Easter Sunday, parallels the Christian doctrine of Christ's descent into hell. The fact that Dante returns to the world on Easter Sunday, after also having seen Heaven, shows that the chronology of the Inferno and indeed the entire Divine Comedy is meant to parallel the facts of Christ's death and Resurrection.