The German theologian, John Peter Lange, effectively demonstrates why the six days mentioned in Exodus 20:11 should be thought of as God’s divine-days or epochs:
“…the Fourth Commandment: ‘…six days shalt thou labor and do all thy work, …for in six days the Lord made heaven and earth.’ …a careful study shows that there is something more than first strikes us. It might be replied that there is no difference of radical idea… but a vast difference in the scale. God’s days of working, it is said, must be the same with man’s days of working, because they are mentioned in such close connection. Then God’s work and man’s work must also be the same, or on the same grade for a similar reason.
The Hebrew word is the same for both: ‘In six days shalt thou labor and do (asah) all thy work; for in six days the Lord made (asah, made, wrought) heaven and earth.’ Is there no transition here to a higher idea? And so of the resting: ‘The seventh shall be to thee a Sabbath (shabath, a rest), for the Lord thy God rested (shabath) on the seventh day,’ – words of the same general import, but the less solemn or more human term here applied to Deity.”
“What a difference there must have been between God’s work and man’s work, – above all, between God’s ineffable repose and the rest demanded for human weariness. Must we not carry the same difference into the times, and make a similar ineffable distinction between the divine working-days and the human working-days of our lower chronology? …The lower, or earthly, day is made a memorial of the higher. We are called to remember by it. In six (human) days do all thy work; for in six (divine) days the Lord made heaven and earth. …It is the manner of the Scriptures thus to make times and things on earth representatives, or under-types, of things in the heavens, – Heb. 9:23. Viewed from such a standpoint these parallelisms in the language of the Fourth Commandment suggest of themselves a vast difference between the divine and the human days, even if it were the only argument the Bible furnished for that purpose. As the work to the work, as the rest to the rest, so are the times to the times” (John Peter Lange, A Commentary on the Holy Scriptures – Genesis, 1868, pp.135-136).