Please read Genesis. The sun was created on the fourth day. Saying that the previous days were 24 hour earth rotation days in relation to the sun is pure speculation.
14 ¶ And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:
15 and let them be for lights in the firmament of the heaven to give light upon the earth: and it was so.
16 And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.
17 And God set them in the firmament of the heaven to give light upon the earth,
18 and to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good.
19 And the evening and the morning were the fourth day.
Genesis was written for humans, not God. The creation account is written in a frame of reference as if a human were atnding on the earth at that time. The creation account of Genesis si exactly what a man would have seen at that time, with human eyes. As God stretched out the heavens (space) He added energy to space (let there be light), and space absorbed that energy and expanded, like a sponge, and reflected excess energy. I suspect this is the “background radiation’s” source. The light at that time may have been so bright, that the light from the sun and stars may have been blocked for a few days, until the light faded and they could be made out.
Evening and morning, the first day. Saying creatures lived millions of years in the day only, or the evening only is the real speculation. The Bible says day, it is a day.
3 And God said, “Let there be light,” and there was light. 4 God saw that the light was good, and He separated the light from the darkness. 5 God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning—the first day.
Sorry, I did react a little fast, without thinking about the sun and the first day, I have to wath myself at times. That being said my previous post to you stands.