In Leviticus 23, Passover completely precedes the Feast of Unleavened Bread, with the first day being a day of convocation:
[Lev 23:5-8 NLT] (5) "The LORD's Passover begins at sundown on the fourteenth day of the first month. (6) On the next day, the fifteenth day of the month, you must begin celebrating the Festival of Unleavened Bread. This festival to the LORD continues for seven days, and during that time the bread you eat must be made without yeast. (7) On the first day of the festival, all the people must stop their ordinary work and observe an official day for holy assembly. (8) For seven days you must present special gifts to the LORD. On the seventh day the people must again stop all their ordinary work to observe an official day for holy assembly."
But the disciples don't begin preparations for the Passover until the first day of the feast of unleavened bread rather than attending the convocation, apparently intending to eat the Passover on the second day of the feast.
[Mat 26:17-20 NLT] (17) On the first day of the Festival of Unleavened Bread, the disciples came to Jesus and asked, "Where do you want us to prepare the Passover meal for you?" (18) "As you go into the city," he told them, "you will see a certain man. Tell him, 'The Teacher says: My time has come, and I will eat the Passover meal with my disciples at your house.'" (19) So the disciples did as Jesus told them and prepared the Passover meal there. (20) When it was evening, Jesus sat down at the table with the twelve disciples.
Did the schedule change by the first century?
These are some data I discovered in doing my own research:
- there seems to be confusion throughout the scriptures concerning the schedule!:
[Mar 14:1 NKJV] (1) After two days it was the Passover and [the Feast] of Unleavened Bread. And the chief priests and the scribes sought how they might take Him by trickery and put [Him] to death.
[Luk 22:1 NKJV] (1) Now the Feast of Unleavened Bread drew near, which is called Passover.
[Num 28:17 NKJV] (17) 'And on the fifteenth day of this month [is] the feast; unleavened bread shall be eaten for seven days.
[Eze 45:21 NKJV] (21) "In the first [month], on the fourteenth day of the month, you shall observe the Passover, a feast of seven days; unleavened bread shall be eaten.
This is a modern Jewish source, delineating Pesach from Passover - very important to understand.
Regarding the preparations for the feast of unleavened bread (the cleansing the homes of leaven), the Jewish Encyclopedia notes that the date of the cleansing might be moved:
This "investigation" was transferred to the eve of Sabbath when the 14th of Nisan coincided with the Sabbath.
The Passover must be killed in the temple, in the evening:
[Deu 16:6 NLT] (6) You must offer it only at the designated place of worship--the place the LORD your God chooses for his name to be honored. Sacrifice it there in the evening as the sun goes down on the anniversary of your exodus from Egypt.
They were also to eat it in the temple:
[Deu 16:7 NLT] (7) Roast the lamb and eat it in the place the LORD your God chooses. Then you may go back to your tents the next morning.
Also, it appears that the "seven days" end a day early:
[Exo 12:14-20 NLT] (14) "This is a day to remember. Each year, from generation to generation, you must celebrate it as a special festival to the LORD. This is a law for all time. (15) For seven days the bread you eat must be made without yeast. On the first day of the festival, remove every trace of yeast from your homes. Anyone who eats bread made with yeast during the seven days of the festival will be cut off from the community of Israel. (16) On the first day of the festival and again on the seventh day, all the people must observe an official day for holy assembly. No work of any kind may be done on these days except in the preparation of food. (17) "Celebrate this Festival of Unleavened Bread, for it will remind you that I brought your forces out of the land of Egypt on this very day. This festival will be a permanent law for you; celebrate this day from generation to generation. (18) The bread you eat must be made without yeast from the evening of the fourteenth day of the first month until the evening of the twenty-first day of that month. (19) During those seven days, there must be no trace of yeast in your homes. Anyone who eats anything made with yeast during this week will be cut off from the community of Israel. These regulations apply both to the foreigners living among you and to the native-born Israelites. (20) During those days you must not eat anything made with yeast. Wherever you live, eat only bread made without yeast."