I don't trust punctuation, brother - it wasn't inspired. Not a single line of the Greek, Hebrew, or Aramaic was punctuated.
The comma is not necessary to understand the plain meaning of the words.
No one hearing, and no one who read this when it was recorded later was thinking that Jesus was announcing to anyone what day he was speaking. That was not a normal way to talk.
If you can find something similar in literature it would not support that THIS speaker is doing that.
To determine if THIS speaker is announcing the day in which he is speaking you would want to find an example where he was known to do such a thing as a manner or personal style of speaking. Did he have a habit of starting out sentences with "Truly I tell you Today.. .etc etc..?"
Or does this speaker have a habit of saying "Today such and such will happen?"
The example that you do have of this particular speaker the day before shows that he is known for telling someone what will occur on
this day and not that he was doing the talking on
this day.
Luke 22
34Jesus answered, “I tell you, Peter, before the rooster crows
today, you will deny three times that you know me.”
Luke 23
42Then he said, “Jesus, remember me when you come into your kingdom.
d ”
43Jesus answered him, “Truly I tell you
today you will be with me in paradise.”
As you can easily see this speaker has a recent habit of using the three words
TODAY YOU WILL to mean what will happen that day.
Therefore you have strong evidence that is the way he spoke and meant it on the cross.
Not only this, but you must also consider, that he was in excruciating pain from crucifixion which is known for the victims to have a very difficult time getting a breath because of the way their weight pulls down on the cross, and many die from suffocation on the cross because of how difficult it is to get a breath which usually is happening at this final stage that he is suffering right before he gives up the ghost.
And so knowing that he would be having a difficult time breathing and being in agony when he speaks these words, common sense tells us that it would be extremely doubtful that he would waste unnecessary superfluous words telling the thief
what day he was speaking.
Is there a danger that the thief might think Jesus was telling him this yesterday? Why would he need to make sure that his hearer would know what day he was speaking? It doesn't fit the context.
The thief would be confused. He would think that Jesus saying "I am talking to you today" would be unnatural and unnecessary information since of course he already knows that Jesus is speaking to him today, so he would discount that as a possible meaning and would understand Jesus as saying "Truly I tell you today you will be with me in Paradise" means he would be in paradise today.
No comma needed but if there was one it would not change how the thief would have understood him.
The only way the thief would have understood Jesus to mean it the way you are trying to tell us it should be understood would be if Jesus said "Truly I tell you today,
('someday', or 'one day,' or 'in the resurrection') you will be with me in paradise" But without adding any other words and saying only what he did as recorded in the text it is impossible that the thief understood him to mean anything other than that he would be in paradise today.
And I believe that he was even if you don't understand how. We are not given the details. We have to wait and find out later.