This may sound like a silly question at first, but I honestly can't decide for myself. I've always assumed that where the text says "And there was evening, and there was morning—the *n*th day" that this is the same day in which the events depicted in the preceding verse take place. E.g., God's actions in Gen.1:1-4 occurred on the 'first day' referred to in Gen.1:5.
But it occurred to me that Hebrew days begin at dusk. Therefore, might not the correct reading be that the events of Gen.1:1-4 take place, then Day One begins with evening and morning in line Gen.1:5? In this scenario the events of Day One are actually Gen.1:6-7 where God separates the waters above from the waters below.
So where precisely does the first day begin? The more times I read the verses, the more reasons I think of how either way might be justified, so I'm curios what the experts have to say.