I have always wondered how it calculate out? First you need to understand that a day actually began at sunset not at midnight the way we celebrate now. The year that Jesus was crucified, Passover was on Wednesday (our Tuesday evening). In the 24 hour period he was "tried, convicted, crucified and buried." It was the beginning of a Holy Day although not Sabbath. Due to the Holy Days that fell that year, it was after Sabbath before the women could "legally" prepare Jesus body for burial. So he was a full 72 hours in the grave before his resurrection.
I have added a link to a visual created by Pastor Dowell that explains in more detail the differences between the current Christian celebration versus the historic holy days that affected the actual events.
Traditions: We live and die by our traditions. But as time goes by traditions are affected by politics and what makes people more comfortable. As a child, there were no stores open on Sundays. Restaurants closed by 2PM. Then more families became two income families. The prosperous times left people buying more things, needing more money, and working more days in the week. Through the pressures of society stores began staying open on Sundays to accommodate people that could only shop on the weekends. The tradition of Sunday afternoon family time changed.
Schools stayed away from scheduling any activities on Sundays because it was sacred to family and church. With the disintegration of the family, the traditions of the family fell apart even more. I am sure everyone can come up with traditions that have changed and/or disintegrated over time. The celebration of the resurrection of Jesus Christ has changed over the years as well. Despite the changes, let us remember the most important thing!
HE IS RISEN! HE IS RISEN INDEED! Jesus, the lamb of God, was crucified for our sins. The blood shed through his death paid for our sins, yours and mine! But he did not remain in the grave. He overcame death and ascended to heaven. Jesus lives today and for those who have faith and belief in him, their sins are forgiven and they can live reconciled to God.