And the evening and the morning were the first day. Genesis 1:5
"Genesis 1 quite clearly depicts God creating the world in six 24-hour days. While old-earth creationists like Hugh Ross
argue that the creation days could be long periods of time, this finds
no support in the Hebrew text.
OT scholar Gordon Wenham, though he
denies that Genesis 1 is chronological history, makes this clear with respect to Genesis 1:
There can be little doubt that here [Genesis 1] “day” has its basic sense of a 24-hour period. The mention of evening and morning, the enumeration of the days, and the divine rest on the seventh show that a week of divine activity is being described here. Elsewhere, of course, “in the day of” and similar phrases can simply mean “when” (e.g., Gen 2:4; 5:1, etc.). Ps. 90:4 indeed says that a thousand years are as a day in God’s sight. But it is perilous to try to correlate scientific theory and biblical revelation by appeal to such texts. Rather, it is necessary to inquire more closely into the literary nature of Gen 1 and whether chronological sequence and scientific explanation are the narrator’s concern.
However, the Scriptures go further than merely depicting a six-day timeframe for God’s creative activity. They plausibly assert it self-referentially." CMI