Why the ninth hour?

From the sixth hour until the ninth hour darkness came over all the land. About the ninth hour Jesus cried out in a loud voice, "Eloi, Eloi, lama sabachthani?"—which means, "My God, my God, why have you forsaken me?" Matthew 27:45 - 46

Everyday at the ninth hour which corresponds to our 3 PM a priest would slay a lamb then climb the Temple and sound the shofar to announce to the citizens of Jerusalem that the sacrifice had been completed and to call the people to prayer.

It was at the ninth hour that Elijah prayed down fire on the sacrifice on Mount Carmel 1 Kings 18. It was the ninth hour when Ezra led the people in prayer of confession and intercession Ezra 9:5. It was at the ninth hour that Daniel opened his window and prayed Daniel 9:21. It was at the ninth hour that Peter and John went into the Temple to pray and there they healed the lame man. Acts 3:1 Cornelius was praying at the ninth hour Acts 10:31. It is easy to see the significance of the ninth hour.

However, it was at this time that Jesus was on the cross. When the ninth hour came instead of the sound of the shofar there was the cry from the cross "It is finished." This signaled that the sacrifice had been completed. Not only was the sacrifice completed for that day but for all eternity. It was only fitting that as the Lamb that was sacrificed for our sins would die at the ninth hour the hour of sacrifice of a lamb for the sins of the people.