It seems that the earth had been established in orbit around the sun and was a globe covered with water before the six days, or periods, of special creative works began.
“There was darkness upon the surface of the watery deep.” Gen 1:2 At that early point, something perhaps a mixture of water vapor, other gases, and volcanic dust must have prevented sunlight from reaching the surface of the earth.
The Bible describes the first creative period this way: “God proceeded to say, ‘Let there be light’; and gradually light came into existence,” or reached the surface of the earth. Gen 1:3
The expression gradually came accurately reflects a form of the Hebrew verb involved, denoting a progressive action that takes time to complete.
Anyone who reads the Hebrew language can find this form some 40 times in Genesis chapter 1, and it is a key to understanding the chapter.
What God began in the figurative evening of a creative period, or age, became progressively clear, or apparent, after the morning of that day. Also, what was started in one period did not have to be fully completed when the next period began.
To illustrate, light gradually began to appear on the first day, yet it was not until the fourth creative period that the sun, moon, and stars could have been discerned.