His death on the cross was the last day in the sense that you're talking about because He said "It is finished", but that's not "the last day" that was being talked about in this thread. That future "last day" is this one:
John 6:40 For my Father’s will is that everyone who looks to the Son and believes in him shall have eternal life, and I will raise them up at the last day.
John 12:48 There is a judge for the one who rejects me and does not accept my words; the very words I have spoken will condemn them at the last day.
The above verses speak of the future last day that will be the last day of earth as we know it. It will be the day that the dead are resurrected and the wicked are condemned.
Scripture teaches that the resurrection of the dead will occur when Christ returns at His second coming at the last trumpet (1 Cor 15:20-23, 50-54) and John 6:40 indicates that will occur "at the last day". Do you agree with that?
Scripture teaches that the day of judgment will occur when Christ returns (Matt 13:40-43, Matt 16:27, Matt 25:31-46) and John 12:48 says that will occur "at the last day". Do you agree with that?
Any one talking about the OT last day were talking about the Cross. Do you agree with that?
Now you have to decide the resurrection of the dead. Because it is only the dead, those who have salvation only in themselves, who rejected Christ, who are raised on the last day, as Jesus taught. No one, because no one was told, but only John saw it and experienced the first Resurrection in Revelation 20:4. No one in the OT knew about this soon (to us today, not them) coming resurrection. Jesus did not teach this resurrection. No one in the NT knew of this resurrection. It only happens after the battle of Armageddon, and John is the only human on earth who has been there, and done that. That is why John put the disclaimer at the end of each of the 7 letters he sent to the literal churches in Asia. No one in history was supposed to claim that the book of Revelation happened until the events in the book actually begin to happen. The first event being the 1st seal. The seals only happened this year, but it seems no one will care or understand except in hindsight after it is too late. Everyone has an opinion, even the early church fathers and their theology. Satan also has been allowed to sow false theology in the last 1990 years.
To reject the next 1000 years as the Day of the Lord is the thing that John made the least symbolic so no one would ever say it is only symbolism, yet some have. He did not even call it the Day of the Lord, because that is a very symbolic term that has several connotations. It is 1000 years and only a 1000 years, nothing more, nothing less. There is a Resurrection at the start. There is a resurrection at the end. The end of the last 1000 years is the last day, with no more days left. This is the resurrection to avoid, not look forward to. The only Resurrection of importance was the one at the Cross. Until the rapture, then such choice will be taken away, never offered again. Only God and the Lamb choose who will be resurrected in Revelation 20:4. And no dead people in the grave before God reaps the final harvest, because they already made the choice. In the last 42 months, choice will be returned and those who choose to not take the mark and choose to be beheaded will be the last humans to be resurrected in Revelation 20:4.
No one will be able to choose to stay home instead of showing up at the battle of Armageddon. Their choice is sealed in Death on that day at the battle of Armageddon. The choice to be marked (branded) and worship Satan had been made in those 42 months. The only thing Amil get right is all will die on that day. To contradict that point is the post rapture belief that humans can endure without being beheaded. No one will be around to rapture. They all have been marked, to endure to that point. They decided not to be beheaded, because beheadings is not defined in enduring. Yet their choice was to be marked instead. Their life was saved, not their soul.
It seems clear to me that to endure was to keep trusting God, and not follow false teachings. Nothing physical to the endurance Jesus taught. Now why did they not spiritualize that endurance along with every other literal idea that was spiritualized?