What the Bible says about Ba Erev
(From Forerunner Commentary)
This sacrifice was made at the beginning of Nisan 15—at ba erev ["even" (KJV); "twilight" (NKJV)]—not at the beginning of the 14th. That makes it very certain that what is being discussed is the first day of Unleavened Bread.
John W. Ritenbaugh
The Night to be Much Observed