"Saturday" (Roman time, midnight to midnight) and "Sunday" (Roman time, midnight to midnight) are actually technically not correct. It is a false dichotomy. The 7th day the Sabbath of the LORD is from even to even (sunset to sunset).
For instance:
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.
The
"evening" begins the day, as given by God.
"Even" is defined by scripture:
Mark 1:32 And
at even,
when the sun did set, they brought unto him all that were diseased, and them that were possessed with devils.
Therefore,
"even" is when
"the sun did set".
The scripture is even more specific, a few of the many examples I may cite yet still in future:
Genesis 15:12 And when
the sun was going down, a deep
sleep fell upon Abram; and, lo, an horror of
great darkness fell upon him.
Genesis 15:17 And it came to pass, that, when
the sun went down, and
it was dark, behold a smoking furnace, and a burning lamp that passed between those pieces.
Judges 19:9 And when the man rose up to depart, he, and his concubine, and his servant, his father in law, the damsel's father, said unto him, Behold, now
the day draweth toward evening, I pray you tarry
all night: behold,
the day groweth to an end, lodge here, that thine heart may be merry; and
to morrow get you early on your way, that thou mayest go home.
Judges 19:25 But the men would not hearken to him: so the man took his concubine, and brought her forth unto them; and they knew her, and abused her
all the night until the morning: and when the day began to spring, they let her go.
Job 38:12 Hast thou commanded
the morning since thy days; and caused
the dayspring to know his place;
Psalms 104:20 Thou makest
darkness, and
it is night: wherein all the beasts of the forest do creep forth.
Psalms 104:21 The young lions roar after their prey, and seek their meat from God.
Psalms 104:22
The sun ariseth, they gather themselves together, and lay them down in their dens.
Psalms 104:23
Man goeth forth unto his work and to his labour until the evening.
John 11:9 Jesus answered, Are there not
twelve hours in the day? If any
man walk in the day, he stumbleth not, because
he seeth the light of this world.
John 11:01 But if
a man walk in the night, he stumbleth,
because there is no light in him.
There are still more as needful.
Hebrews 3-4 is clear.
Hebrews 4:3,
"my (God's) rest" and
"the works were finished from the foundation of the world", which is a direct reference to Genesis 2:1-3. It even uses the word
"finished". God rested the 7th day in Genesis 2:1-3. It is His rest, the 7th day, the sabbath (rest) of the LORD thy God, Exodus 20:8-11.
Hebrews 4:4,
"he spake in a certain place of the seventh day on this wise, And God did rest the seventh day from all his works", which
"certain place" is Genesis 2:1-3; re-cited in Exodus 20:8-11. The 7th day the sabbath (rest) of the LORD thy God.
Hebrews 4:5,
"my (God's) rest)", citing Psalms 95, which is citing Genesis 2:1-3; Exodus 20:8-11, etc. Again, this is the 7th day the sabbath (rest) of God at Creation in Genesis 2:1-3.
Hebrews 4:6,
"remaineth", from when?
"from the foundation of the world" as per Hebrews 4:3 and thus it is not new, but has been around from the beginning.
Hebrews 4:9,
"rest", sabbatismos, literally and truly sabbath keeping in scripture and in all known extant Greek sources, dictionaries, and so on and again
"remaineth".
Hebrews 4:10,
"his (God's) rest", which is the 7th day the sabbath (rest) of the LORD thy God from Genesis 2:1-3., "as God did from his (works)", which "
works were finished from the foundation of the world" as per Hebrews 4:3.
Hebrews 4:11,
"that rest" (ie God's rest), the 7th day the sabbath (rest) of the LORD thy God.
Look around by using the "search" option on Hebrews 3-4, and there is found even a whole thread on Hebrews 3 - 4 that seems to have been around awhile now that has gone into this in some considerable depth-
Hebrews 3-4 [KJB], the 7th Day the Sabbath of the LORD JEHOVAH - "my rest" "remaineth" to My people.
You may of course disagree, as is your prerogative, but that is no evidence of being correct, nor of being defensible from (or foundational upon) scripture itself.