They are referenced as normal days in other parts of the Bible. For instance, in the 4th commandment:
“Remember the Sabbath Day, to keep it holy. SIX DAYS you shall labor and do all your work. But the SEVENTH DAY is the Sabbath of the LORD your God. In it, you shall do no work. . .For in SIX DAYS the LORD made the heavens and the earth, the sea, and all that is in them; and rested the SEVENTH DAY. Therefore the LORD blessed the Sabbath DAY and hallowed it.” (emphasis mine)
He gives the six days of creation and the one day of rest as the reason for the Sabbath. Had the days been eons or something, we’d be resting for six eons and then resting for one, obviously preposterous.
So I don’t question at all what a “day” is.