first month, on the fourteenth day of the month ... the fifteenth day of the same month

The first month of the Hebrew calendar marks when Yahweh brought the Israelites out of Egypt. The fourteenth day and fifteenth day are around the beginning of April on the Western calendar. (See: rc://en/ta/man/translate/translate-hebrewmonths and rc://en/ta/man/translate/translate-ordinal)

at twilight

"at sunset"