On this day from sunrise till sunset Passover preparations were made as the start of Passover were 14 Nisan at 6 pm, the Passover meal had to be observed. (the Hebrews’ days according to YHWH S calender starts at sunset and ends at sunset).
In the 13th many things are done :
Preparing the lamb
Exodus 12; 6And ye shall keep it up until the fourteenth day of the same month: and the whole assembly of the congregation of Israel shall kill it in the evening.
8And they shall eat: