The following shows God's requirement for His passover. Jesus became our passover sacrificed for us per Apostle Paul, so Christ's crucifixion had... to align with the Old Testament passover requirements, and it did.
Ex 12:5-18
5 Your lamb shall be without blemish, a male of the first year: ye shall take it out from the sheep, or from the goats:
6 And 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.
Jesus was crucified on the 14th of Nissan, which at evening was the required time of the lamb sacrifice. At sunset would begin Nissan 15, the 1st day of the feast, which was to be a high day (sabbath).
7 And they shall take of the blood, and strike it on the two side posts and on the upper door post of the houses, wherein they shall eat it.
8 And they shall eat the flesh in that night, roast with fire, and unleavened bread; and with bitter herbs they shall eat it.
9 Eat not of it raw, nor sodden at all with water, but roast with fire; his head with his legs, and with the purtenance thereof.
10 And ye shall let nothing of it remain until the morning; and that which remaineth of it until the morning ye shall burn with fire.
11 And thus shall ye eat it; with your loins girded, your shoes on your feet, and your staff in your hand; and ye shall eat it in haste: it is the LORD's passover.
12 For I will pass through the land of Egypt this night, and will smite all the firstborn in the land of Egypt, both man and beast; and against all the gods of Egypt I will execute judgment: I am the LORD.
13 And the blood shall be to you for a token upon the houses where ye are: and when I see the blood, I will pass over you, and the plague shall not be upon you to destroy you, when I smite the land of Egypt.
They were to eat the passover that night (the 15th which began at sunset 14th). That was the first day of the feast.
14 And this day shall be unto you for a memorial; and ye shall keep it a feast to the LORD throughout your generations; ye shall keep it a feast by an ordinance for ever.
God described that day of eating the passover as a feast to be kept forever.
15 Seven days shall ye eat unleavened bread; even the first day ye shall put away leaven out of your houses: for whosoever eateth leavened bread from the first day until the seventh day, that soul shall be cut off from Israel.
16 And in the first day there shall be an holy convocation, and in the seventh day there shall be an holy convocation to you; no manner of work shall be done in them, save that which every man must eat, that only may be done of you.
That is what John 19 is referring to about the "high day". The 1st day of the feast was to be a high day, a sabbath. That began at sunset on the 14th right after the lamb was sacrificed at evening on the 14th. Must use the Hebrew reckoning for a day, sunset to sunset.
17 And ye shall observe the feast of unleavened bread; for in this selfsame day have I brought your armies out of the land of Egypt: therefore shall ye observe this day in your generations by an ordinance for ever.
18 In the first month, on the fourteenth day of the month at even, ye shall eat unleavened bread, until the one and twentieth day of the month at even.
KJV