TimeLine Note:
Jesus was born on Nisan 6, 2 BC and He died at age 34 years 8 days on Nisan 14, 33 AD - the 14th Day of God's 5th Millennium.
This chart may be helpful with calculations involving both BC and AD dates.
If you understand why Jesus had to become a man, had to come to Earth and had to fulfill His mission; and if you understand what that mission was; then you likely know that Jesus came here to fulfill the Old Testament - the Old Covenant that God made with Israel.
This fulfillment also applied to the Law of the Old Covenant, which was but a foreshadow of what lay ahead - Jesus and His New Covenant.
Jesus became the Spotless Lamb, taking the place of the spotless sacrificial lamb of the Passover, and died in place of the sinner, making the payment for sin that we, just like that symbolic lamb, could never have made.
Fulfilling Passover meant fulfilling it in detail, including the timing. The lamb was to be sacrificed on the 14th day of the Jewish first month, Nisan (also Abib), just before dusk, and just before evening, which begins the new day of Nisan 15. So Jesus needed to be sacrificed at that same time.
He also needed to rise three days later as He said He would, and that day needed to be the Day of First Fruits, on the First Day of the Week.