Here are some of the verses where the Septuagint uses the phrase "between the two
evenings".  We can take this as historical reference, if we cannot accept it otherwise.  
The Septuagint is much older than the Masoretic Manuscripts used for translating the

Exodus 12.6, "And it shall be kept by you till the fourteenth of this month, and all the multitude of the
congregation of the children of Israel shall kill it <toward> evening."

Leviticus 23.5, "In the first month, on the fourteenth day of the month, between the evening times is
the Lord's Passover."

Numbers 9.3, "On the fourteenth day of the first month at even, thou shalt keep it in its season; thou
shalt keep it according to its law, and according to its ordinance."

Numbers 28.4, "Thou shalt offer one lamb in the morning, and thou shalt offer the second lamb
towards evening."

Numbers 28.8, "And the second lamb thou shalt offer toward evening;...."

Exodus 16.12, "I have heard the murmuring of the children of Israel:  speak to them, saying, Towards
evening ye shall eat flesh, and in the morning ye shall be satisfied with bread;..."

It is significant that the translators of the Septuagint, (translated in the reign of Ptolemy
Philadelphus 285-247 BC) even then understood that "between the two evenings" was
<toward evening>.  Perhaps Leviticus 23:5 is even more telling.  “Between the evening
times” conveys the time between the beginnings of the two evenings.  The first evening
began at noon and the second evening began at sunset.  This has to be so otherwise the
statement is confusion.  For, if we think of the first and second evenings as blocks of time
in relation to this statement no time exists at all.  In other words, the term expresses a
figure of speech.