Let me quote Genesis 1:1–5 (emphasis mine):

In the beginning, God created the heavens and the earth. The earth was without form and void, and darkness was over the face of the deep. And the Spirit of God was hovering over the face of the waters. And God said, “Let there be light,” and there was light. And God saw that the light was good. And God separated the light from the darkness. God called the light Day, and the darkness he called Night. And there was evening and there was morning, the first day. (Genesis 1:1–5, ESV)

• The earth did not have form and was void. Hence, we cannot think that the round, sphere-like Earth as we see today was created yet. Therefore, we are forced to interpret “the earth” written above as the ‘substance’ for earth.
• The Sun was not created yet. Only light was created and was separated from darkness.

Conclusion: Honest reading of this passages strongly indicates that the “evening” and the “morning” recorded here is not the usual evening and morning as we see today. Indeed, the Hebrew word ‘yom’ (which is translated as ‘day’ here) when used in the Scripture sometimes denoted a time frame longer than 24 hours. Therefore there isn’t much ground to believe that the ’1st day’ written in verse 5 indicates a 24 hour day.