The expression, "when they were created," indicates as it seems, an indeterminate time not accurately described. But this argument will confute those authors who calculate a certain number of years reduced to one, from the time when it is possible that the world may have been created. And again, the expression: "This is the book of the generation," is as it were indicative of the book as it follows, which contains an account of the creation of the world; in which it is intimated that what has been related about the creation of the world is consistent with strict truth.
Why the Torah Refuses to Date Creation Precisely
The Midrash of Philo 4:2