The word day is used later in the Scriptures as well and its meaning is clear. Israel was instructed to count off days for festivals, etc. These actual days as defined by both today's standards and those from the beginning are recognized as such in even as late as the NT Scriptures.
You cannot add meanings to a word such as day only because of disbelief or one can eventually write off all of Scripture as fables and tales by one's own choosing.
I Corinthians 4:5-6:
5 Therefore judge nothing before the appointed time; wait until the Lord comes. He will bring to light what is hidden in darkness and will expose the motives of the heart. At that time each will receive their praise from God.
6 Now, brothers and sisters, I have applied these things to myself and Apollos for your benefit, so that you may learn from us the meaning of the saying, “Do not go beyond what is written.”
All I'm saying is that, the verses quoted have non literal words incorporated into the language.
Let's go back to the verse:
And God said, “Let there be lights in the firmament of the heavens to separate the DAY from the NIGHT"
Literally real lights are placed into (not above or below but into, like nails in a cork board) a non-literal dome? Then the non-literal dome separates the literally real day and night?
I would say that, this is just a broken exegesis.
It's trying to make literally true what was never intended by God to be received as such by us in modern scientific times. No more would God have intended that we believe that a solid dome exists in the sky that God might expect us to believe in 6 24-hour rotating planet based days of creation.
I would say it's just a misunderstanding to suggests that God intended to convey to us that such things are literally real, windows in the firmament holding back water, stars stuck "in" the dome, equidistant, that birds fly across the flat face of the firmament or that God in human form in Ezekiel might walk upon the top of the firmament, like frozen water, like ice, like pavement, like molten metal, like sapphire etc.
Taking these concepts in the old testament literally, I would say it's just a mistake in exegesis. It's just not God's intent in scripture to convey these concepts as a scientifically modern literal reality. And that includes the idea of a spherical earth rotating in space 6 times while moving around the sun. These are modern scientific advanced perspectives. And we can't read our modern perspectives into a historical/ancient near-east narrative.
And once people reach this point of understanding in their spiritual journey, only then can they really begin to re-construct their faith in a way that can make sense of these concepts. But without reaching first base, they won't be able to make sense of positions at second or third bases.