שלום
The length of days are significant but not upmost significant. Here's why.
Most of us understand that breisheet (genesis/origins) are well aligorical. This is to say HaSh-m created the earth in seven days, signifying the seventh as the shabbat(day of rest).
More over, let's look deeper. He created the darkness and light. And He chose light. Are you seeing the pattern? Sanctification or the act of seperating.
Up until day 6, I've heard many rebbe state that each day could've lasted thousands of years. Yet, day seven only twenty four hours.
Good read. Upvoted you. May your wisdom exceed your performance.
Differentiation is what I referred to it as, or the "act of separating" and then sanctifying is a repeated theme in each of the days highlighted above.