Since Genesis 1 does not record the creation of the sun until the 4th day, that might be some indication that the meaning of "evening", "morning" and "day" in Genesis 1:5 is something other than literal. How can there be a literal 24-hour day without the sun?
You can have light without the sun. Morning and evening are TIME based events. God created time and then later the sun. In heaven, as Christians, we know there will be no more sun or moon but Jesus Christ will be the light thereof. There are other sources of light than sun. Yet, the plants need sun to survive, hence the literal day.