You are showing your ignorance. The Creation scriptures define a day as "evening and morning". The creation story is referred to in several subsequent passages as occurring in "six day". The Catholic church just caved into liberalism.
Hey I thought the world when first created was without day and night?
Okay so you have now defined a day in terms of an evening and a morning. How long is an evening and how long is a morning? Did a evening and morning take exactly the same amount of time 20 million years ago as it does today? From where are you measuring this day? On Earth or at the Center of creation or outside of time? Ever hear of Einstein and relativity? Is God's time the same as ours? Some theologians and physicists believe that everything that was ever created or will be created already exists and the reason that God knows the future is because God is outside of time and space.
Odd that there is no evening to the seventh day...
How can humans put a time frame on God's morning or evening? Could be a day, a year, or millions of years. Who are we to say?
Nope, they just remembered the Scripture, "a thousand years in Thy sight are but as yesterday when it is past." And the way Christians and Jews approached the Scriptures before rationalism introduced the idea of 'literal' interpretation--as if a work written over centuries in different cultures under the influence of a radically transcendant God would just be readable at face value as if it were written by and for post-'Enlightenment' rationalist.
St. Basil the Great, writing in the fourth century, was hardly a prisoner of 'liberalism', and in his Hexaemeron wrote, "It matters not whether you day 'day' or 'aeon', the thought is the same."
St. Gregory of Nyssa described the opening chapters of Genesis as "Doctrine in the guise of a narrative."
Nor did the medieval Jewish sages Maimonides and Nachmonides see the opening of Genesis as a literal history--their commentaries focus on the fact that it is the opening of the Torah and the odd construction in the 'first day': the Hebrew does not use an ordinal, but translates as "one day".