Genesis 1 defines a day:
God called the light Day, and the darkness he called Night. And there was evening and there was morning, the first day. (Genesis 1:5 ESV)
Exodus 20 gives us another point of reference:
Six days you shall labor, and do all your work, but the seventh day is a Sabbath to the LORD your God. On it you shall not do any work, you, or your son, or your daughter, your male servant, or your female servant, or your livestock, or the sojourner who is within your gates. For in six days the LORD made heaven and earth, the sea, and all that is in them, and rested on the seventh day. Therefore the LORD blessed the Sabbath day and made it holy. (Exodus 20:9-11 ESV)
Certainly it makes more sense to hold that these texts are not equivocating, that “a day is a day,” rather than some unspecified lengthy period of time.
Creation is a real-life story, not a machine. For it to have an honest-to-goodness literary backstory rather than a mechanistic one is just what we should expect.