What is the measure of the six days mentioned in the verse: "Indeed, your Lord is Allah, who created the heavens and the earth in six days and then established Himself above the Throne," if there was no earth or sun to define the meaning of "day"?

The Almighty's saying: (He created the heavens and the earth in six days) does not necessitate that the estimation of a day be based on the movement of celestial bodies or the sun and moon, for that is an estimation for worldly days. Before the creation of the sun and moon, there was another measure for estimating time, just as there are different time measures like the light-year. Ibn al-Jawzi and Ibn Taymiyyah mentioned that the six days mean "the measure" of that, and that they are days and a time estimated by a movement other than that of the sun and moon, and estimated by the movement of bodies that existed before the creation of the heavens and the earth.