by The Watchman

Take a look at what these well known jewish encylopedias have to say on
the day.
The Jewish Encyclopedia (under the topic day) In the Bible, the season
of light (Gen. i. 5), lasting "from dawn [lit. "the rising of the
morning"] to the coming forth of the stars" (Neh. iv. 15, 17). The term
"day" is used also to denote a period of twenty-four hours (Ex. xxi.
21). In Jewish communal life part of a day is at times reckoned as one
day; e.g., the day of the funeral, even when the latter takes place late
in the afternoon, is counted as the first of the seven days of mourning;
a short time in the morning of the seventh day is counted as the seventh
day; circumcision takes place on the eighth day, even though of the
first day only a few minutes remained after the birth of the child,
these being counted as one day. Again, a man who hears of a vow made by
his wife or his daughter, and desires to cancel the vow, must do so on
the same day on which he hears of it, as otherwise the protest has no
effect; even if the hearing takes place a little time before night, the
annulment must be done within that little time. The day is reckoned from
evening to evening-i.e., night and day-except in reference to
sacrifices, where daytime and the night following constitute one day
(Lev. vii. 15)

As I showed in my Scriptural Study, "WHAT IS THE SCRIPTURAL DAY?", the
day is the light as YHWH declared it to be. It begins with the first
sight of light over the horizon and ends at nightfall. The last sentence
in this paragraph doesn't even make sense. The so called jewish scholars
want us to believe that a day is from evening to evening except for
sacrifices.
Encylopedia Judaica
The third biblical calendar, which is first attested in Zechariah 1:7
and 7:1, employs the Babylonian month names, which go back to the
calendar of Nippur that antedated Hammurapi. According to rabbinic
tradition, these names were imported by those who returned to the land
of Israel from the Babylonian Exile (TJ, RH 1:2, 56d). It is most likely
that these immigrants also introduced the lunar-solar calendar and the
intercalation of a month to reconcile the lunar and solar years, a
characteristic of the Babylonian calendar. The adoption of the
Babylonian calendar was also responsible for the custom of reckoning the
day from the previous evening. (Encyclopedia Judaica under Topic "Year"
and "Day")

Now isn't that interesting. The day beginning with the previous evening
came from Babylon.
The Encyclopedia of Jewish Symbols (under the topic Sun)
The Jewish calendar is both lunar and solar, attuned to the agricultural
cycles governed by solstices and equinoxes, as well as the monthly
rhythms of the waxing and waning moon. The Jewish day begins at sunset,
a practice probably adopted during the Babylonian exile (the 6th century
B.C.E.)

Another admittance as to when the evening to evening was adopted.
Babylonian Origins of 'Sunset to Sunset' Day