The sainting of Popes John XXIII and John Paul II will happen at the same time Sunday morning, when Pope Francis decrees it to be so at a Vatican ceremony expected to attract near one million people.
The ceremony -- expected to start at about 9:30 AM in Rome (3:30 AM Eastern) -- will itself be relatively short, expected to last around three hours.
Celebrations will begin with the solemn chant of the litany of the saints, while some 150 cardinals, 1,000 bishops, and 6,000 priests process through St. Peter's Square towards the steps at the base of the Vatican basilica. It is unknown if Pope Benedict XVI, who the Vatican confirmed on Saturday would be attending, will also process with the group.
Following the procession, the head of the Vatican Congregation for the Causes of Saints, Cardinal Angelo Amato, will ask Francis in front of those gathered three times to make the deceased pontiffs saints.
Assenting after the third petition, Francis will decree in Latin:
"By the authority of our Lord Jesus Christ ... after due deliberation and frequent prayer for divine assistance, and having sought the counsel of many of our brother bishops, we declare and define Blessed John XXIII and John Paul II be saints and we enroll them among the saints, decreeing that they are to be venerated as such by the whole church."
Like that, the key part of Sunday's celebration will be finished. The assembled group will then continue to celebrate Mass for the Second Sunday of Easter, which John Paul II also declared be Divine Mercy Sunday.
The first reading for the Mass is from the Acts of the Apostles and details the life of the Apostles following Jesus' death and resurrection.
"The faithful all lived together and owned everything in common; they sold their possessions and shared out the proceeds among themselves according to what each needed," it reads at one point.
The Gospel for the day is taken from John and recalls Jesus' visit to the apostles following his resurrection. According to the Gospel, Jesus mystically appeared to the apostles as they were hidden in a locked room, saying: "Peace be with you."
Another key moment comes during the prayers of the faithful, where those present will pray for new Saints John and John Paul's intercession.
The prayer for John's help asks that the Lord "through the prayers of Saint John XXIII, help the leaders of nations, in their thoughts and decisions, to reject every escalation of hatred and violence; may all human relations reveal the victory of Jesus risen and alive."
The prayer for John Paul's help asks that the Lord "through the prayers of Saint John Paul II, continue to inspire a passionate commitment to human dignity among men and women of culture, science and government; in every person may honor be given to Jesus risen and alive."
Likewise, the two new saints will be referenced in the Eucharistic prayer Sunday for the first time, being referred to as "Saints John and John Paul."
Otherwise, the celebration will continue as a Mass. Distribution of communion is expected to take up the longest amount of time, with some 270 deacons assisting the thousands of priests and bishops in distributing the sacrament.
Those distributing are to be stationed all the way down the Via della Conciliazione, the main road leading from the Vatican to Rome's city center, to the banks of the Tiber river -- a 15-minute walk from St. Peter's Basilica.