These seven days do not include the period of our planet’s creation and preparation as a dwelling place for man. They are limited to Earth’s ‘temporal existence,’ that is, to Time, considered as distinct from Eternity.”So is 200,000 years (or 4 billion years) a period of time or is it of eternal length?
Something to notice here is that the physical creation of the earth is doctrinally placed where (and LDS) one traditionally thinks of the spiritual creation. So perhaps the words "temporal" and "Time" have a context which is merely that which spans the Lord's dealings with humanity on earth that is relevant to us; Adam to the present.
Seems to me the quote is saying exactly the opposite of what you want it to say. "Eternity" does not have duration. 200,000 years is by definition a duration of time. Therefore 200,000 years is not eternal, merely a long duration. Therefore you are wrong.
Considering the context, it doesn't appear that I am wrong (perhaps you meant that the doctrine is wrong?). Whether I am wrong or not, it doesn't change the fact that the OP is wrong, because the doctrine on D&C 77 is clear that the dispensations do not cover the entire length of the earth's physical existence.