The people who had returned from exile celebrated Passover on the fourteenth day of the first month of the following year. 1
References for Ezra 6:19
6.19 Ex 12.1-20.
All the priests and the Levites had purified themselves and were ritually clean. The Levites killed the animals for the Passover sacrifices for all the people who had returned, for the priests, and for themselves.
The sacrifices were eaten by all the Israelites who had returned from exile and by all those who had given up the pagan ways of the other people who were living in the land and who had come to worship the Lord God of Israel.
For seven days they joyfully celebrated the Festival of Unleavened Bread. They were full of joy because the Lord had made the emperor of Assyria favorable to them, so that he supported them in their work of rebuilding the Temple of the God of Israel.