“A “day” measures the time it takes for the sun to rotate on its axis.”
(I assume you mean the time it takes for the EARTH to rotate upon its axis).
God defines “day.” He said He created light, I quote:
Then God said, “Let there be light”; and there was light. And God saw the light, that it was good; and God divided the light from the darkness. God called the light Day, and the darkness He called Night. So the evening and the morning were the first day. (Genesis 1:3)
So, that was the first “day.” It was the light of the first period of time, divided by the darkness. Nothing about the spin of an axis.
Now, the next “day,” as defined by God:
Then God said, “Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.” Thus God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament; and it was so. And God called the firmament Heaven. So the evening and the morning were the second day. (Genesis 1:6-8)
Light; darkness; in the meantime the firmament (heavens) is formed, the waters collected. Another day. No apparent spinning of an axis, as there is still no earth.
We get the earth on the third day, I quote:
“Then God said, “Let the waters under the heavens be gathered together into one place, and let the dry land appear”; and it was so. And God called the dry land Earth, and the gathering together of the waters He called Seas. And God saw that it was good. Then God said, “Let the earth bring forth grass, the herb that yields seed, and the fruit tree that yields fruit according to its kind, whose seed is in itself, on the earth”; and it was so. And the earth brought forth grass, the herb that yields seed according to its kind, and the tree that yields fruit, whose seed is in itself according to its kind. And God saw that it was good. So the evening and the morning were the third day.
It is on the third day we can have an axis, as we now have an earth. A busy day, really, the seas formed and all the plants. Now we are spinning, presumably. 24 hours, approximately. It is still called a day.
And since then and ever since then a day has meant about a 24 hour period of time, with a period of sunrise and a period of night.
No evolution could have been possible until the 3rd day, anyway. There were no living things, except God Himself, until then.