For more on this topic and many other science "vs." Scripture topics read:
The Science of God: The Convergence of Scientific and Biblical Wisdom by Gerald L. Schroeder.
Time differs from one location to another because time is governed by gravity and velocity. The following timeline is based on exactly 24 hour periods as measured by universal time, the cosmic clock (frequency of cosmic background radiation - CBR - the echo of the big bang).
The first six days of Genesis can NOT be guided by earth based time since for the first two days the earth had not even existed yet! Only after the creation of Adam does the Scriptural narrative switch to earth based time (time as perceived by human beings).The length of days only seem to shorten as the six days of creation progress because of our particular earth based perspective. As we see it, the progressive shorting of the days is due to the expansion of the universe.
For more on this topic and many other science "vs." Scripture topics
read:
The
Science of God: The Convergence of Scientific and Biblical Wisdom by Gerald
L. Schroeder.