I'm not sure I understand what you're asking, but I'll try to explain what I meant.
If the early earth had an atmosphere that was dense with ash or debris (from heavy volcanic activity and impacts with other objects), then it may have been so thick that sunlight could not reach the surface. When He said "Let there be light," it may have just been when the atmosphere cleared up and allowed light to reach the surface. Separating the day and the night just describes the rotation of the earth, but the fact that light only hits the surface when it faces the sun would not have been evident from that vantage point until the sky cleared enough to let light through.
I think that makes way more sense than saying he created the sun after creating the earth. It sounds like you're suggesting it could mean he created the sun first, but created sunlight after, but that also makes no sense to me. I probably misunderstood you though. Care to clarify?