The length of days in Genesis Chapter 1 is rigorously the same as today: 24 hours, with the same length. In the first three days there was an equinox situation, the light-dark alternation is provided by God himself through the appearance and withdrawal of light throughout the space. During those days the light did not depend on the sun obviously, but that did not mean at all that when there was no time, or that that time was quite different than today (presumably much higher, though it could be shorter also!) All seven days are prototype week and lasted equally among themselves and with those of today. The celestial movements of the stars (sun, moon) are the same as time and space and have not undergone any change related to sin or other natural causes (disasters, flood, earthquakes, meteors, etc.)....