Would you agree that by the 4th day he had defined a 24 hour day?
Gen 1:16And 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.
Gen 1:17And God set them in the firmament of the heaven to give light upon the earth,
Gen 1:18And to rule over the day and over the night, and to divide the light from the darkness: and God saw that [it was] good.
Gen 1:19And the evening and the morning were the fourth day.
I don`t know why he`d define a day as 24 hours after the third day but defined it as thousands of years for the 1st 2nd & 3rd days.
But he`s God.
I suppose he can do what he wants.