If to God, a thousand years is as one day, and one day as a thousand years, and man, who reckons a day as a constant divided into 24 parts called hours... how do you know it was the 24-hour definition if there was no man to witness it? With 1000 years = one day, that means it could be 1000 years or 86 1/2 seconds. But that double equivalency really means that God has no time boundaries, and he could call any phase a day, using it like Grandma Walton ["In my day....."]
I have written on this in the old Science forum. Why would God not create and then take was we call "time" to enjoy his creation without all the nonsense, vanity, and stubbornness of the creatures he had always intended to create that are like himself, who think they can take his words and then know everything, like when Jesus told his disciples to beware the Pharisees' yeast and they thought he was talking about bread?