How do we understand the timing of the Great 3 Days?

If Jesus died on Friday and rose on Sunday, how do we understand three days?

Christians celebrate the saving events of Jesus Christ's suffering, death and resurrection over a period we call the Great Three Days, (Triduum in Latin). 

The gospels all attest that Jesus rose from the dead early on the first day of the week.

Matthew 28:1: "After the Sabbath, as the first day of the week was dawning…"

Mark 16:1-2: "When the Sabbath was over… very early on the first day of the week, when the sun had risen…"

Luke 24:1: "On the first day of the week at early dawn…"

John 20:1: "Early on the first day of the week, while it was still dark."

The first day of the week is Sunday. In that culture, as throughout the Bible, the day begins with sunset, not sunrise and not midnight. Sabbath ended at sundown on Saturday. Just after sundown, Sunday began. 

Three days is not necessarily 72 hours. "Hours" as we think of them were not a unit of measure then. It means three distinct days as delineated by sundowns and sunsets.

The vast majority of the world's Christians, including United Methodists, have used the following means to arrive at the timing of our celebrations during Holy Week. 

• Thursday evening: Last Supper and Great Commandment.  After sundown marks the beginning of the first day (Eve of Friday). Jesus is arrested and tried.
• Friday morning: First day continues, and Jesus is executed, removed from the cross and buried.
• Friday sundown: Second day begins. (Eve of Sabbath/Saturday).
• Saturday (sunrise to sunset): Jesus lies in the tomb.
• Saturday sundown: Third day begins. (Eve of Sunday).
• Sunday morning: Third day continues and Jesus is raised from the dead.

This way of reckoning the time of Holy Week has been consistent in Christian practice, East and West, from at least the third century A.D.