When I left my house today, it was “still dark” – ie, there were stars out, etc. But within a minute or two, it was already starting to be light. Dawn was clearly coming, although it did not arrive for about ten minutes. By the time I got where I was going, it was “just after dawn,” although the sun was hidden behind trees and hills, and it was not terribly bright.
Now, if I was telling the story of a big event this morning, how dark and light was it? Do I eat a lot of Vitamin A foods, or am I blind as a bat in dusk conditions? Do I remember more the pre-dawn quiet, or the racket of the dawn chorus (actually absent this morning, because a storm is coming and the birds were a bit reluctant to stir from cover), or the light coming between hills and dazzling my eyes, or what? And that is in a period of about 10-20 minutes.
And the city of old Jerusalem was actually smaller than my plat, so the women would probably have gotten to the tomb faster than I did.
Memory and the recounting of memory tells you a lot about the witness, as well as about the event.
In this case we are also dealing with a Jewish culture accustomed to believe that slightly varied impressions were normal in the vicinity of an appearance made by God, and that those variations should be valued as prophetic experiences with revelatory implications. So if Woman 1 remembers dawn, that is about “newness”, while Woman 2’s memory of darkness implies things like “endings” or “the people who walked in darkness.” That is complementary revelation, not contradiction. So of course the Evangelists wanted to record it all.