Unknown to most followers of Yahweh, there is a remarkable witness that provides evidence for the practice of the 7-day Festival of Passover and Unleavened Bread occurring on Abib 14-20.
This witness comes from an extra-biblical work, the Book of Yashar, also known as Sefer Ha-Yashar.
The present copy of the Book of Yashar is by no means to be assigned the authority of Scriptures. However, what the text says regarding the Passover of the Exodus nevertheless proves quite informative and interesting.
Book of Yashar
81:5 And the children of Israel TRAVELED FROM EGYPT AND FROM GOSHEN AND FROM RAMESES, AND ENCAMPED IN SUCCOTH ON THE FIFTEENTH DAY of the first month.