I find it fascinating that God created light on day 1, but the sun was not created until day 4. Although this troubles some, we know that light can exist independently of the heavenly bodies. Although we today look to the sun to demonstrate to us the clear difference between night and day, God speaks of periods of night and day even before the sun existed. I cannot fully explain this, since God did not choose to elaborate, but I believe it to be possible nevertheless. The heavenly bodies apparently mark the days, but they do not make them! Night can exist without us observing the moon, and likewise Day can exist without us observing the sun. As a side note, it should be observed that throughout the creation account each day is defined as "the evening and the morning." The Hebrews reckoned their days this way (evening first and then morning), but we reverse the order.
The phrase "it was good" is used six times in this chapter ("it was very good" is used once). All of God's works are good for the purpose He plans for them. God does not need to test or experiment with what He is making, like an unskilled craftsman. His words accomplish precisely what He intends for them to accomplish (cf. Isa. 55:11).
The Hebrew word used here for "day" is yom. Reputable lexicographers have long affirmed that the references to "the first day", "the second day", etc. can only mean a 24 hour period, and not some long "age" (as has been hypothesized by some in an effort to stretch the age of the Earth into millions or billions of years). There is no need Biblically (or scientifically) to have an old Earth. There is no reason why Exodus 20:11 should not be taken at face value. God created everything in six literal days--not six eons of time. Although the use of the word yom may be ambiguous in some contexts, it is never ambiguous when preceded by a numeral (as is the case in Gen. 1). In such a case, it can only refer to a 24 hour period. Besides, if one were to believe that each "day" here is really an eon of time, what would the "years" of 1:14 possibly represent? Such a position leads to foolishness, and this is also seen in the creation of mankind. Is it reasonable to affirm that man was made during a sixth eon of time (day six), and he lived all the way through a seventh eon of time (day seven--in which God rested)? How could Adam live even through one eon of time lasting millions or billions of years? Such is absurd. It is philosophically impossible to understand the word "day" in this context in any other sense than as a period of 24 hours.