Exodus 12:6, At twilight [Heb. erev, or between the evenings]. This phrase can have several meanings.

Loosely speaking, according to first century Jewish tradition, this would have been the time from high noon when the sun is at its zenith when it starts to descend toward the horizon until approximately 6 PM when it disappears behind the horizon (The Life Time of Jesus, by Alfred Edersheim, p. 813; Hednrickson, 2002). From 12 noon onward is not the literal meaning of the Hebrew word erev though.

According to The TWOT, erev means “dark or evening and refers to sunset or evening” and applies to the actual darkening of the skies at twilight as the sun is beginning to sink behind the horizon. Therefore, between the evenings can also mean “between the evening of the 13th day of the first month going into the 14th day of the first month and the 14th day going into the 15th day.” That is to say, the entire daylight portion of the 14th day or Passover day could be the period between the two evenings.

With this understanding, it is not difficult to see how Yeshua and his disciples keeping the Passover or Lord’s Supper at the beginning of the 14th day is still called “the Passover” in the Gospels, even though the majority of the Jews traditionally ate the Passover meal at the end of the 14th going into the 15th.