The Biblical day starts at night fall.

All quoted Bible texts come from the King James Authorized Version out of the Online Bible computer program. Any notations in the form "[pg. nn]" denote the page from the book by Ron Bierer, "The True Bible Sabbath," from which I have drawn specific information.

Old Testament evidence

The Biblical day is measured from sundown to sundown, being in order of evening (night) then morning (daylight).

Genesis 1:5 And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.

This ordering is repeated in Genesis 1 verses 8, 13, 19, 23, and 31. Also:

Leviticus 23:32 It shall be unto you a sabbath of rest, and ye shall afflict your souls: in the ninth day of the month at even, from even unto even, shall ye celebrate your sabbath.

That the Biblical day begins with night is confirmed in the book of Nehemiah, where the gates are closed at the coming of nightfall and the next day, a Sabbath:

The pattern for a day being night followed by daylight is followed in Psalm 55:

Joshua slew five men and hanged them on trees, but  

Deuteronomy 21:
22* 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:
23* 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 God;) that thy land be not defiled, which the LORD thy God giveth thee for an inheritance.

Joshua 10:
26* And afterward Joshua smote them, and slew them, and hanged them on five trees: and they were hanging upon the trees until the evening.
27* 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.

Samson riddled the Philistines which they were to answer within the seven days of a feast (verse 12), which they encouraged his wife to plead from him the answer, and which answer they gave to Samson on the seventh day before the sun went down.

Judges 14:
12* And Samson said unto them, I will now put forth a riddle unto you: if ye can certainly declare it me within the seven days of the feast, and find it out, then I will give you thirty sheets and thirty change of garments:
13* But if ye cannot declare it me, then shall ye give me thirty sheets and thirty change of garments. And they said unto him, Put forth thy riddle, that we may hear it.
14* And he said unto them, Out of the eater came forth meat, and out of the strong came forth sweetness. And they could not in three days expound the riddle.
15* And it came to pass on the seventh day, that they said unto Samson's wife, Entice thy husband, that he may declare unto us the riddle, lest we burn thee and thy father's house with fire: have ye called us to take that we have? is it not so?
16* And Samson's wife wept before him, and said, Thou dost but hate me, and lovest me not: thou hast put forth a riddle unto the children of my people, and hast not told it me. And he said unto her, Behold, I have not told it my father nor my mother, and shall I tell it thee?
17* And she wept before him the seven days, while their feast lasted: and it came to pass on the seventh day, that he told her, because she lay sore upon him: and she told the riddle to the children of her people.
18* And the men of the city said unto him on the seventh day before the sun went down, What is sweeter than honey? and what is stronger than a lion? And he said unto them, If ye had not plowed with my heifer, ye had not found out my riddle.

New Testament evidence

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"Day" can mean both the whole day (light and dark) and also just the light part. That’s why one can say a day is starting when nightfall comes.

Lets move on.Numbers 28. vs. 3-4...sacrifices were offered morning and evening, starting in the morning. Using moon reckoning this would be 2 different days.

Read Mark 4 vs.35. I know there is a true sabbath{rest} yet for his people, which the 7th day business is but a type and shadow of the real.
Hebrews 4. and then read
Isaiah 11 vs. 10.

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Matthew 27:
57* ¶ When the even was come, there came a rich man of Arimathaea, named Joseph, who also himself was Jesus' disciple:
58* He went to Pilate, and begged the body of Jesus. Then Pilate commanded the body to be delivered.

Luke 23:54 That day was the preparation, and the Sabbath drew on.

They
had to hurry to get the body down and removed as the sun was going down,
and the High Sabbath was about to begin.

Mark 15:42* ¶ And now when the even was come, because it was the preparation, that is, the day before the sabbath,

John 19: 31* ¶ The Jews therefore, because it was the preparation, that the bodies should not remain upon the cross on the sabbath day, (for that sabbath day was an high day,) besought Pilate that their legs might be broken, and that they might be taken away.

Matthew 28:1* ¶ In the end of the sabbath, as it began to dawn toward the first day of the week, came Mary Magdalene and the other Mary to see the sepulchre.

Matthew 28:1* ¶ In the end <1161> <3796> of the sabbath <4521>, as it began to dawn <2020> toward <1519> the first <3391> day of the week <4521>, came Mary Magdalene and the other Mary to see the sepulchre.

Note Luke 23:54 Epiphosko is translated "draw on,"

Mark 16:
1* ¶ And when the sabbath was past, Mary Magdalene, and Mary the mother of James, and Salome, had bought sweet spices, that they might come and anoint him.
2* And <2532> very <3029> early in the morning <4404> the first <3391> day of the week <4521>, they came unto the sepulchre at the rising <393> of the sun <2246>.

Luke 24:1* ¶ Now <1161> upon the first <3391> day of the week <4521>, very early in the morning <3722> <901>, they came unto the sepulchre, bringing the spices which they had prepared, and certain others with them.

John 20:1* ¶ <1161> The first <3391> day of the week <4521> cometh Mary Magdalene early <4404>, when it was <5607> yet <2089> dark <4653>, unto the sepulchre, and seeth the stone taken away from the sepulchre.

John ch. 20 vs. same thing...it was the 8th day , the day after the sabbath.

John 20:19* ¶ Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace be unto you.

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This passage shows that the day is recognized as starting at night:

Acts 27:
27* But when the fourteenth night was come, as we were driven up and down in Adria, about midnight the shipmen deemed that they drew near to some country;
* * *
33 And while the day was coming on, Paul besought them all to take meat, saying, This day is the fourteenth day that ye have tarried and continued fasting, having taken nothing.

The error of dividing the day at noon: As Ron Bierer points out [pg. 50], this division of days by sundown is practical being that most work is done by daylight for which Sabbaths give workers a full work period to rest. A day divided at noon, which some claim is where the sun is 'even' between the rising and setting horizons, would cause workers to work every daylight period - half days before and after Sabbath - not giving them a full day's rest.

Again, 'even' or 'evening', from the Hebrew word "ereb" (Strong's #06153) meaning "dusk" or "sundown" [pg. 51], is some time near night-fall when shadows are long:

Strong's Definitions - from Online Bible

06150 bre `arab aw-rab' - from Online Bible
a primitive root [identical with 06148 through the idea of covering with a texture]; TWOT-1689; v
AV-evening 2, darkened 1; 3
1) to become evening, grow dark
   1a) (Qal) to become evening, grow dark
   1b) (Hiphil) to spend the evening, do at evening

06153 bre `ereb eh' -reb - from Online Bible
from 06150; TWOT-1689a; n m
AV-even 72, evening 47, night 4, mingled 2, people 2, eventide 2, eveningtide+06256 2, Arabia 1, days 1, even+0996 1 evening+03117 1, evening+06256 1, eventide+06256 1; 137
1) evening, night, sunset
   1a) evening, sunset
   1b) night

06751 llu tsalal tsaw-lal' - from Online Bible

a primitive root [identical with 06749 through the idea of hovering over (compare 06754)]; TWOT-1921; v
AV-began to be dark 1, shadowing 1; 2
1) to be or become or grow dark
   1a) (Qal) to become or grow dark
   1b) (Hiphil) to shadow

.

303 ana {an-ah'}
a primary prep and adv;; prep
AV - by 3, apiece 2, every man 2, each 1, several 1, two and two + 1417 1, among 1, through 1, between 1, by 1, in 1; 15
1) into the midst, in the midst, amidst, among, between

393 anatello {an-at-el'-lo}
from 303 and the base of 5056; TDNT - 1:351,57; v
AV - be up 2, rise 2, spring up 1, make rise 1, at the rising of 1, spring 1, arise 1; 9
1) rise
1a) to cause to rise
1a1) of the earth bring forth plants
1b) to rise, arise, to rise from, be descended from
1b1) of sun moon and stars)

901 bathus {bath-oos'}
from the base of 939;; adj
AV - deep 2, very early in the morning + 3722 1; 3
1) deep

939 basis {bas'-ece}
from baino (to walk);; n f
AV - foot (sole of) 1; 1
1) a stepping, walking
2) that with which one steps, the foot

1909 epi {ep-ee'}
a root;; prep
AV - on 196, in 120, upon 159, unto 41, to 41, misc 338; 895
1) upon, on, at, by, before
2) of position, on, at, by, over, against
3) to, over, on, at, across, against

2014 epiphaino {ep-ee-fah'-ee-no}
from 1909 and 5316; TDNT - 9:7,1244; v
AV - appear 3, give light 1; 4
1) to show to or upon
   1a) to bring to light
2) to appear, become visible
   2a) of stars
3) to become clearly known, to show one's self

2017 epiphausko {ep-ee-fows'-ko}
a form of 2014; TDNT - 9:310,*; v
AV - give light 1; 1
1) to shine upon
   1a) Christ will pour upon you the divine truth as the sun gives light to men aroused from sleep

2020 epiphosko {ep-ee-foce'-ko}
a form of 2017; TDNT - 9:310,1293; v
AV - begin to dawn 1, draw on 1; 2
1) to grow light, to dawn

2089 eti {et'-ee}
perhaps akin to 2094;; adv
AV - yet 52, more 34, any more 5, still 4, further 4, longer 3, misc 15; 117
1) yet, still
   1a) of time
      1a1) of a thing which went on formerly, whereas now a different state of things exists or has begun to exist
      1a2) of a thing which continues at present
         1a2a) even, now
      1a3) with negatives
         1a3a) no longer, no more
   1b) of degree and increase
      1b1) even, yet
      1b2) besides, more, further

2094 etos {et'-os}
apparently a primary word;; n n
AV - year 49; 49
1) year
For Synonyms see entry 5843

3391 mia {mee'-ah}
irregular feminine of 1520;; adj
AV - one 62, first 8, a certain 4, a 3, the other 1, agree + 4160 + 1106 1; 79
1) only one, someone

3722 orthros {or'-thros}
from the same as 3735;; n m
AV - early in the morning 3; 3
1) daybreak, dawn
2) at early dawn, at daybreak, early in the morning

3735 oros {or'-os}
probably from an obsolete oro (to rise or "rear", perhaps akin to 142, cf 3733); TDNT - 5:475,732; n n
AV - mountain 41, mount 21, hill 3; 65
1) a mountain

3796 opse {op-seh'}
from the same as 3694 (through the idea of backwardness); (adverbially) late in the day;; v
AV - in the end 1, even 1, at even 1; 3
1) after a long time, long after, late
   1a) late in the day, i.e. at evening
   1b) the sabbath having just passed, after the sabbath
      1b1) at the early dawn of the first day of the week

4253 pro {pro}
a primary preposition; TDNT - 6:683,935; prep
AV - before 44, above 2, above ... ago 1, or ever 1; 48
1) before

4404 proi {pro-ee'}
from 4253;; adv
AV - in the morning 5, early in the morning 2, early 2, morning 1; 10
1) in the morning, early
2) the fourth watch of the night, from 3 o'clock in the morning until 6 o'clock approximately

4639 skia {skee'-ah}
apparently a primary word; TDNT - 7:394,1044; n f
AV - shadow 7; 7
1) shadow
   1a) shade caused by the interception of light
   1b) an image cast by an object and representing the form of that object
   1c) a sketch, outline, adumbration

4653 skotia {skot-ee'-ah}
from 4655; TDNT - 7:423,1049; n f
AV - darkness 14, dark 2; 16
1) darkness
2) the darkness due to want of light
3) metaph. used of ignorance of divine things, and its associated wickedness, and the resultant misery in hell

4655 skotos {skot'-os}
from the base of 4639; TDNT - 7:423,1049; n n
AV - darkness 32; 32
1) darkness
   1a) of night darkness
   1b) of darkened eyesight or blindness
2) metaph.
   2a) of ignorance respecting divine things and human duties, and the accompanying ungodliness and immorality, together with their consequent misery in hell
   2b) persons in whom darkness becomes visible and holds sway

5056 telos {tel'-os}
from a primary tello (to set out for a definite point or goal); TDNT - 8:49,1161; n n
AV - end 35, custom 3, uttermost 1, finally 1, ending 1, by (one's) continual + 1519 1; 42
1) end
   1a) termination, the limit at which a thing ceases to be (always of the end of some act or state, but not of the end of a period of time)
   1b) the end
      1b1) the last in any succession or series
      1b2) eternal
   1c) that by which a thing is finished, its close, issue
   1d) the end to which all things relate, the aim, purpose
2) toll, custom (i.e. indirect tax on goods)

5316 phaino {fah'-ee-no}
prolongation for the base of 5457; TDNT - 9:1,1244; v
AV - appear 17, shine 10, be seen 2, seem 1, think 1; 31
1) to bring forth into the light, cause to shine, shed light
2) shine
   2a) to shine, be bright or resplendent
   2b) to become evident, to be brought forth into the light, come to view, appear
      2b1) of growing vegetation, to come to light
      2b2) to appear, be seen
      2b3) exposed to view
   2c) to meet the eyes, strike the sight, become clear or manifest
      2c1) to be seen, appear
   2d) to appear to the mind, seem to one's judgment or opinion
For Synonyms see entry 5837

4521 sabbaton {sab'-bat-on}
of Hebrew origin 07676; TDNT - 7:1,989; n n
AV - sabbath day 37, sabbath 22, week 9; 68
1) the seventh day of each week which was a sacred festival on which the Israelites were required to abstain from all work
   1a) the institution of the sabbath, the law for keeping holy every seventh day of the week
   1b) a single sabbath, sabbath day
2) seven days, a week

5457 phos {foce}
from an obsolete phao (to shine or make manifest, especially by rays, cf 5316, 5346); TDNT - 9:310,1293; n n
AV - light 68, fire 2; 70
1) light
   1a) the light
      1a1) emitted by a lamp
      1a2) a heavenly light such as surrounds angels when they appear on earth
   1b) anything emitting light
      1b1) a star
      1b2) fire because it is light and sheds light
      1b3) a lamp or torch
   1c) light, i.e brightness
      1c1) of a lamp
2) metaph.
   2a) God is light because light has the extremely delicate, subtle, pure, brilliant quality
   2b) of truth and its knowledge, together with the spiritual purity associated with it
   2c) that which is exposed to the view of all, openly, publicly
   2d) reason, mind
      2d1) the power of understanding esp. moral and spiritual truth
For Synonyms see entry 5817

5817:
Synonyms
   See Definition for auge       827
   See Definition for pheggos   5338
   See Definition for phos      5457

   5457 - the general term for light: light of a fire
   5338 - is a more concrete and emphatic term: the bright sunshine, the beam of light
    827 - is a still stronger term, suggesting the fiery nature of light; used of shooting, heating rays