"But at the place which Yahweh thy Elohim shall
choose to place his name in, there thou shalt sacrifice the passover
at even [ba-ereb], at the going down
of the sun , at the season that thou
camest forth out of Egypt."
It is important to understand what this phrase means. Notice the phrase does not say "sunset" or "sundown," but "at the going down." That means the sun was on its way down, but had not reached that point yet. It was "going" down, but not gone. The verse says to sacrifice the Passover as the sun is going down. It does not say to sacrifice the Passover after the sun has set. The sun is only "going down" at the end of a day, not the beginning.
Proof that this phrase can mean "prior to sunset" is found by studying two verses in the book of Joshua wherein the same Hebrew phrase occurs.
Josh.8:29 , "And the king of Ai he hanged on a tree until eventide [ereb]: and as soon as the sun was down , Joshua commanded that they should take his carcase down from the tree, and cast it at the entering of the gate of the city, and raise thereon a great heap of stones, that remaineth unto this day."
Josh.10:26,27 , "... and they were hanging upon the trees until the evening [ereb]. And it came to pass at the time of the going down of the sun, that Joshua commanded, and they took them down off the trees, and cast them into the cave wherein they had been hid, and laid great stones in the cave's mouth, which remain until this very day."
The underlined words in both verses are the equivalent Hebrew of "at the going down" in Deut.16:6. Notice one verse says the sun was already down and the other verse says it was going down. To understand what the status of the sun really was, we must look at the commandment that led Joshua to order the king's body taken down. It is found in Deut.21:22,23;
"And if a man have committed a sin worthy of death, and he be to be put to death, and thou hang him on a tree: His body shall not remain all night upon the tree, but thou shalt in any wise bury him that day ; (for he that is hanged is accursed of Elohim;) that thy land be not defiled, which Yahweh thy Elohim giveth thee for an inheritance."
Yahweh commanded the body to be removed and buried the same day . To accomplish that, the body had to be removed before sunset . After sunset would have been a new day. Josh.8:29 should have been translated "at the going down of the sun" just as Deut.16:6 and Josh.10:27 were. This also shows that the word "ereb" in Josh.8:29 and 10:27 has the meaning of "before sunset" in these cases.