Numbers 9:11
7 And those men said to Moses, “We are ceremonially defiled by the dead body of a man; why are we kept back from offering the Lord’s offering at its appointed time among the Israelites?” 8 So Moses said to them, “Remain here and I will hear what the Lord will command concerning you.” 9 The Lord spoke to Moses: 10 “Tell the Israelites, ‘If any of you or of your posterity become ceremonially defiled by touching a dead body, or are on a journey far away, then he may observe the Passover to the Lord. 11 They may observe it on the fourteenth day of the second month at twilight; they are to eat it with bread made without yeast and with bitter herbs.
2 Chronicles 30:2
1 Hezekiah sent messages throughout Israel and Judah; he even wrote letters to Ephraim and Manasseh, summoning them to come to the Lord’s temple in Jerusalem and observe a Passover celebration for the Lord God of Israel. 2 The king, his officials, and the entire assembly in Jerusalem decided to observe the Passover in the second month. 3 They were unable to observe it at the regular time because not enough priests had consecrated themselves and the people had not assembled in Jerusalem. 4 The proposal seemed appropriate to the king and the entire assembly.
Notes and References
"... Whereas in other passages the command to celebrate the festival of Passover is associated with the memory of the liberation from slavery in Egypt (e.g. Exodus 12:1, 11, 27; Numbers 9:1–3; Deuteronomy 16:1), no theological reason for the festival of Passover is given in Leviticus 23:5. rather, the text states that the festival shall be celebrated “in the first month, on the fourteenth day of the month, at twilight ...” (Leviticus 23:5). this is corroborated by the records of King Josiah’s Passover (2 Chronicles 35:1); and it is also on this date that ezekiel reckons the Passover to be kept (45:21). Furthermore, an indirect reference to the fourteenth of the first month is also understood in the law concerning the second Passover, which is to be kept “in the second month on the fourteenth day, at twilight ...” (Numbers 9:11 ... It is in the second month that King Hezekiah invited the whole of Israel and Judah to keep the Passover; 2 Chronicles 30:2), “they slaughtered the Passover lamb on the fourteenth day of the second month”; 2 Chronicles 30:15) ..."
Saulnier, Stéphane Calendrical Variations in Second Temple Judaism: New Perspectives on the "Date of the Last Supper" Debate (p. 72) Brill, 2012