In the following passage of Scripture, God is speaking of the time when the Israelites ate
Passover.  Observe that this passage speaks of no other time until verse 51, where we see
that God brought the Israelites out of Egypt on the <self-same day> that they ate the
Passover!  In other words, the same day they <ate> the Passover was the same day they
began their journey out of Egypt.  Could anything be plainer?

Ex 12:43  And the LORD said unto Moses and Aaron, This is the ordinance of the Passover: There
shall no stranger eat thereof:
44 But every man's servant that is bought for money, when thou hast circumcised him, then shall he
eat thereof.
45 A foreigner and an hired servant shall not eat thereof.
46  In one house shall it be eaten; thou shalt not carry forth ought of the flesh abroad out of the house;
neither shall ye break a bone thereof.
47  All the congregation of Israel shall keep it.
48  And when a stranger shall sojourn with thee, and will keep the Passover to the LORD, let all his
males be circumcised, and then let him come near and keep it; and he shall be as one that is born in
the land: for no uncircumcised person shall eat thereof.
49  One law shall be to him that is homeborn, and unto the stranger that sojourneth among you.
50  Thus did all the children of Israel; as the LORD commanded Moses and Aaron, so did they.
51 And it came to pass the selfsame (06106) day, that the LORD did bring the children of Israel out of
the land of Egypt by their armies.

Notice the definition for #6106 below.  Then notice Genesis 2.23 below that.

06106 `etsem {eh'tsem}

from 06105; TWOT - 1673c; n f

AV - bone 104, selfsame 11, same 5, body 2, very 2, life 1,
strength 1; 126

1) bone, essence, substance
1a) bone
1a1) body, limbs, members, external body
1b) bone (of animal)
1c) substance, self

Here is an example where this word #6106 is used:

Genesis 2:23  “And Adam said, This is now bone (6106) of my bones (6106), and flesh of my flesh:
she shall be called Woman, because she was taken out of Man.”

According to the definition of this word <self-same> in Exodus 12:43-51, God brought the
Israelites out of Egypt the exact same day they ate the Passover.  We know when they
started out of Egypt – therefore, we know when they ate the Passover – on the 15th day
of Nisan.  The following verse leaves no doubt about that point.

Numbers 33:3  “And they departed from Rameses in the first month, on the fifteenth day of the first
month; on the morrow after the Passover the children of Israel went out with an high hand in the sight
of all the Egyptians.”

Therefore, there is no doubt at all that the Israelites left on the 15th of Nisan, the daylight
portion of the same day that they ate the Passover the night before, which started the
15th of Nisan!