JWs resolve this issue by saying that what happened on day 4 isn't the literal creation of the sun moon and stars but only their being made discernible as distinct objects in the sky. Prior to that sunlight was already reaching the earth's surface from day one when God said let light come to be. Only, the sunlight was diffuse, shining through a haze and one could not make out the sun or any other heavenly body as distinct objects in the sky. They basically teach that what happened on day 4 is the clearing of the atmospheric clouds to allow heavenly objects to be distinctly discernible for the first time.
I've seen that explanation. Unfortunately for them, it's BS. The scriptures don't say anything about haze lifting, or indiscernible objects. It says, Then God said: “Let there be luminaries in the expanse of the heavens to make a division between the day and the night, and they will serve as signs for seasons and for days and years. They will serve as luminaries in the expanse of the heavens to shine upon the earth.” And it was so. And God went on to make the two great luminaries, the greater luminary for dominating the day and the lesser luminary for dominating the night, and also the stars. Thus God put them in the expanse of the heavens to shine upon the earth and to dominate by day and by night and to make a division between the light and the darkness. Then God saw that it was good. And there was evening and there was morning, a fourth day.
The NWT translation (the only translation endorsed by Jehovah, ya know) itself says, God 'went on to MAKE the ...luminaries, and 'put them in the expanse of the heavens...to make a division between the light and the darkness'. Using the WT explanation, there was already a division between light and dark, you just couldn't 'see' the luminary bodies. That's in direct conflict with what the verse said. The scripture is pretty plain - god made em and hung em on the 4th day. (And even that doesn't make sense since it's the 4th 'day' already. What divided the day and night the first three days?)