@gavvet God divided light and darkness so they could constantly and regularly succeed each other. The completion of the first day brought light to the world. The first day of the week was the same day Christ rose from the dead.
The first three days were preparation for the last three, there are open skies, deep oceans and dry land which needed to be occupied. There has been light for three days without the sun. On the fourth day He said; "Let there be lights in the expanse of the sky to separate day from night, and let them serve as signs to mark seasons and days and years. The sun, moon and stars enable us to determine time, months, years and seasons. It is the stars which give us the accurate time of day and not our clocks. Months are measured by the moon and the position of the sun the seasons. The rotation of the earth around the sun, the year. Time on earth is regulated by these lights in the sky. For the traveler, the stars and sun are also a reliable compass.
There are many miracles in the detail of creation, especially in the placement of the lights in the sky and these are all a detailed part of God's plan.
The length of the year,
the distance of the earth from the sun,
the length of seasons,
the time between harvests,
the rate of plant growth,
the intensity of the sunlight,
the reflected light of the moon, for our restful sleep,
the length of day and night.

Yes, the seven days of creation is still a 24 hour period!

Source: Christ in Genesis. The God of Creation
Disciple's Study Bible NIV 1984
@frieda