Note: The Jewish calendar date begins at sundown of the night beforehand. Thus all holiday observances – including the first seder – begin the night before the dates listed. Jewish calendar dates also conclude at nightfall.
So Nisan 15 which is a Thursday the 9th actually begins on Wed. night which is when we should observe it. This note above was taken from a Jewish web site. Google Passover 2009 for more information. The unleavened bread is NEVER eaten on the 14th like the WT teaches since this bread is the actual Passover or sanctified ingredient of the meals for Passover week as it later came to be called in scripture.
Joseph