All of the days in Genesis end thus: ‘And the morning and the evening were the nth day’.
All save one.
Why is that?
God could only count to 6.
Since the 'big bang' is impossible, given these laws, there must be a first cause outside of time (since everything started with the 'big bang'). While secular scientists postulate just about anything to avoid even thinking there might be a (horrors) God in charge, Genesis explains the 'first cause' elegantly and concisely in the first four words: "IN THE BEGINNING, GOD created the heavens and the Earth..."
This man, a physicist, believes that we are currently in the seventh day, if I recall, the day you ask about. He ties young Earth age creation theory (6,000 years) to old Earth creation theory (15+/- billion years) and explains how the Earth can be both 6,000 years of age and also 15 billion years of age. (FWIW, I haven't watched this video in a number of years, so I may have made some errors in my comments about this video.)