In Exodus 12:6-11, it seems quite clear that the lambs should be sacrificed in the afternoon of Nisan 14 and eaten that night, which is Nisan 15 because Jewish days start at night. The Passover meal is to be completed that night as well. I will take all quotes from the online New American Bible found at:
nccbuscc.org/nab/bible/
"You shall keep it until the fourteenth day of this month, and then, with the whole assembly of Israel present, it shall be slaughtered during the evening twilight.
7 They shall take some of its blood and apply it to the two doorposts and the lintel of every house in which they partake of the lamb. 8 That same night they shall eat its roasted flesh with unleavened bread and bitter herbs. 9 It shall not be eaten raw or boiled, but roasted whole, with its head and shanks and inner organs. 10 None of it must be kept beyond the next morning; whatever is left over in the morning shall be burned up. 11
3 "This is how you are to eat it: with your loins girt, sandals on your feet and your staff in hand, you shall eat like those who are in flight. It is the Passover of the LORD.
In Mark 14:12-17, Jesus’s disciples prepare for the Passover “When they sacrificed the Passover lamb” (Nisan 14) and ate the Last Supper that night (Nisan 15). Jesus was then crucified after sunrise on the continuation of Nisan 15.
"On the first day of the Feast of Unleavened Bread, when they sacrificed the Passover lamb,
3 his disciples said to him, “Where do you want us to go and prepare for you to eat the Passover?” 13 He sent two of his disciples and said to them, “Go into the city and a man will meet you, carrying a jar of water.
4 Follow him. 14 Wherever he enters, say to the master of the house, ‘The Teacher says, “Where is my guest room where I may eat the Passover with my disciples?”’ 15 Then he will show you a large upper room furnished and ready. Make the preparations for us there.” 16 The disciples then went off, entered the city, and found it just as he had told them; and they prepared the Passover. 17 When it was evening, he came with the Twelve.
In John 18:28, Jesus is brought before Pilate before Passover (Nisan 14), making the Last Supper occur on the night following Nisan 13 (early Nisan 14 in Jewish days).
"Then they brought Jesus from Caiaphas to the praetorium.
13 It was morning. And they themselves did not enter the praetorium, in order not to be defiled so that they could eat the Passover."This is reaffirmed in John 19:14: "It was preparation day for Passover, and it was about noon.
5 And he said to the Jews, “Behold, your king!”
It seems quite clear that the two accounts are discrepant. Catholic Bible scholars note it as so. Here is the footnote in the NAB for John 18:28:
" [28] Praetorium: see the note on
Matthew 27:27. Morning: literally, “the early hour,” or fourth Roman division of the night, 3 to 6 A.M. The Passover: the synoptic gospels give the impression that the Thursday night supper was the Passover meal (
Mark 14:12); for John that meal is still to be eaten Friday night."
I’m running into space issues, and so I will continue on a separate post.