Outside of Genesis 1, "Day" is used as a singular or plural 410 Times, always = a 24 hour day....
Evening + Morning without the word "Day" is used 38 Times & always used to refer to a 24 hour "Day"...
Night & Day is used 52 Times and always refers to a 24 hour "Day"....
Hence, in Genesis 1, the Bible is referring to literal "Days".....
And the evening and the morning were the first day.
Genesis 1:5