Part 2:
Genesis 2:17 But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
Here we need to put ourselves in the "shoes" (they probably weren’t wearing any – not even sandals – at the time) of Adam. By "day" does God mean the light portion of the 24 hour day, or does he mean the 24 hour day, or is it some indeterminate period of time? How are we to tell? There aren’t any clues in the text. How are we to know? What did Adam think He meant? Did God leave Adam guessing?
Genesis 3:5 For God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil.
What did Satan mean by the word "day"? By "day" did Satan mean the light portion of the 24 hour day, or does he mean the 24 hour day, or is it some indeterminate period of time? How are we to tell? There aren’t any clues in the text. How are we to know? What did Eve think he meant? Did Satan leave her guessing?
Genesis 3:8 And they heard the voice of the LORD God walking in the garden in the cool of the day: and Adam and his wife hid themselves from the presence of the LORD God amongst the trees of the garden.
A little side-bar to our study: when is "the cool of the day"? In the morning. Maybe, the temptation of Adam and Eve took place in the very early hours of the morning.
A second side-bar: one of the neat things about doing these kinds of in-depth studies is that you learn things along the way that you weren’t looking for in the first place!
Genesis 4:14 Behold, thou hast driven me out this day from the face of the earth; and from thy face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass, that every one that findeth me shall slay me.
Which "day" is Cain talking about? How do you prove it from the text? There’s no clues.
Genesis 5:4-5 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters: And all the days that Adam lived were nine hundred and thirty years: and he died.
Notice how we went from "days" to "eight hundred years" and from "days" to "nine hundred and thirty years." The latter terms are specific periods of time and yet they are referred to as "days." The "were" is the only reference, or clue, you have.
Genesis 6:4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
The phrase "in those days" is indeterminate. But, from the text itself (given it says "they bare children") it seems obvious that it isn’t talking about the light portion of the 24 hour day, nor is it talking about a 24 hour day. Given that the previous verses covered the generations that lived up till the time of the Flood it seems obvious that here the word "days" refers to several thousand years.
From here on out we will, for the most part, ignore all uses of the word "day" as either the light portion of the 24 hour day, or the 24 hour day, or for an indeterminate period of time. These are customary uses of the term–this also tells us how far back these concepts go.
Genesis 7:4 For yet seven days, and I will cause it to rain upon the earth forty days and forty nights; and every living substance that I have made will I destroy from off the face of the earth.
Here we have the same two different uses of the word "days" as we saw in Gen. 1:5.
Genesis 7:17 And the flood was forty days upon the earth; and the waters increased, and bare up the ark, and it was lift up above the earth.
Here the word "days" means 24 hour days.