This is why Genesis told us what God meant. "It was evening and morning, the first day."
Absolutely. No question its a 24 hour period. I don’t know how God could make it any clearer.
Genesis 1:5 (KJV)
5 And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
Genesis 1:8 (KJV)
8 And God called the firmament Heaven. And the evening and the morning were the second day.
Genesis 1:13 (KJV) All plant life created here.
13 And the evening and the morning were the third day.
Genesis 1:19 (KJV) Sun created here.
19 And the evening and the morning were the fourth day.
Genesis 1:23 (KJV)
23 And the evening and the morning were the fifth day.
Genesis 1:31 (KJV)
31 And God saw every thing that he had made, and, behold, it was very good. And the evening and the morning were the sixth day.
A better question to consider is what took place between Genesis 1:1 and 1:2? Why did the Earth BECOME formless, empty, covered in water - all forms of judgment.