Contrary to common understanding, which assumes that the Sabbath week of creation intends to indicate the duration of the creation event, Moses used the Sabbath week as a pneumonic literary device.
I observe that the days of the week begin in the evening and extend into daylight. This mirrors the creation story, which starts in darkness and moves into light. Everything that was once disordered, formless, shapeless, and unclear becomes revealed, clarified, understood, and evident as each day unfolds.
Each day brings new levels of clarity and finer detail. During the first three days, several domains are created: outer space, the sky, the seas, and dry land. The following three days focus on populating each domain: celestial bodies inhabit outer space, birds fill the sky, fish populate the oceans, and land creatures inhabit the land. Each creature is designed to thrive in its respective domain.
Moses doesn't intend to tell us how long the process took. Rather, he notices a significant parallel between a day, which moves from darkness to light and God's creative work, which also moves from darkness to light. And the Sabbath week is a handy way to organize the material to make it easier to understand and remember.