what does the bible say?

Let’s examine when Jesus observed the Passover, because we can’t be wrong if we follow His example (1 Peter 2:21).  

In Luke 22:14-15 we read, “And when the hour had come, He sat down, and the twelve apostles with Him.  Then He said to them, ‘With fervent desire I have desired to eat this Passover with you before I suffer.” The Passover was ordained to be an annual event.  It was to be observed yearly on the evening commencing the 14th day of the first month according to the Sacred (or Jewish) calendar. “On the fourteenth day of the first month at twilight is the LORD’S Passover” (Leviticus 23:5).  

Suppose the Israelites in Egypt had observed this ordinance at some other time than that set by God.  They would not have been saved when the death angel passed by that night (Exodus 12:13-14, 22-23)!  God does things on time.  He has given us an exact time for this ordinance.

Many, following the examples of men, have used different hours of the day for this occasion.  But Jesus ate that Passover meal after the sun had set.  On the eve of the Passover – that solemn annual observance kept by all Israel, in anticipation of the sacrifice of the Messiah – Jesus ate His last Passover supper. During supper Jesus instituted the foot washing ceremony (John 13:1-17) and changed the symbols which had existed from the time Israel left Egypt (Exodus 12:1-13), to the bread (broken bread to represent His body broken for our infirmities) and wine (to represent His blood shed for our spiritual sins). With this change of symbolism

Jesus showed how Christians, His true followers, should observe the Passover from that time on.  He also demonstrated, by example, that the Passover should continue to be kept “On the fourteenth day of the first month at twilight…” as it had always been done since its institution in Egypt.