Augustine argues that his own statement is out of harmony with the text of scripture in Genesis 1 and that it is his own external bias that he brings to the text of Genesis 1 that results in his out-of-harmony wrenching of the meaning in the text.
"(God) spoke and they were made, He commanded and they were created. Creation, therefore, did not take place slowly in order that a slow development might be implanted in those things that are slow by nature; nor were the ages established at plodding pace at which they now pass. Time brings about the development of these creatures according to the laws of their numbers, but there was no passage of time when they received these laws at creation"
The Literal Meaning of Genesis, translated by John Hammond Taylor (1982), Vol. 1, Book 4, Chapter 33, paragraph 51–52, p. 141, italics in the original. New York: Newman Press.
"Whoever, then, does not accept the meaning that my limited powers have been able to discover or conjecture but seeks in the enumeration of the days of creation a different meaning, which might be understood not in the prophetical or figurative sense, but literally and more aptly, in interpreting the works of creation, let him search and find a solution with God’s help. I myself may possibly discover some other meaning more in harmony with the words of Scripture."
The Literal Meaning of Genesis, in Lavallee, Louis. 1989. Augustine on the Creation Days, Journal of the Evangelical Theological Society 32, no. 4:464.
no time lapse - but instant creation and a flat denial of some long time process be it 7 days or 70 billion years - is the direction Augustine was going. That T.E.'s think Augustine is making their case is inexplicable! Augustine does not argue that this is the case due to the language of Genesis 1 and 2. He argues it for his own external-to-Genesis-1 reasons.
Sadly for you in that case Ex 20:11 "exists" as God Himself summarized the details in Genesis 1:2-2:3 quite to the contrary of those imagining that Genesis 1 does not describe a literal 7 day week. The expanded form in Ex 20:8-11 makes this "irrefutable in legal code".
And as for the "kind of literature" that it is - in Genesis 1:2-2:3
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Professor James Barr, Regius Professor of Hebrew at the University of Oxford, has written:
‘Probably, so far as I know, there is no professor of Hebrew or Old Testament at any world-class university who does not believe that the writer(s) of Genesis 1–11 intended to convey to their readers the ideas that: (a) creation took place in a series of six days which were the same as the days of 24 hours we now experience (b) the figures contained in the Genesis genealogies provided by simple addition a chronology from the beginning of the world up to later stages in the biblical story (c) Noah’s flood was understood to be world-wide and extinguish all human and animal life except for those in the ark. Or, to put it negatively, the apologetic arguments which suppose the "days" of creation to be long eras of time, the figures of years not to be chronological, and the flood to be a merely local Mesopotamian flood, are not taken seriously by any such professors, as far as I know.’
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That is the opinion of professors not at all inclined to accept the 7 day creation week that we find in Gen 1:2-2:3 yet they can still 'read' and point to the author's intent - whether they agree with the author or not.