I believe that there was no time before the beginning. God created it. We have to understand that the words "And there was evening and there was morning"(NASB), for each of the 6 days of creation must be understood as "there was the eve of a creation, and then there was the beginning of the thing created". It is why it is not mentionned anything about the "evening" before the 7th day, contrary to the 6 days of creation; because the 7th day had no eve, because it was not created, but was the rest, the result of the whole creation having longed "6 days". Now, these 6 days of creation did not long 24 hours each, nor 1000 years each, not even millions of years, because there was not any matter of time, yet, till God decided to create it, for His relations with beings. There was no time before He created it, because God doesn't need time for Himself. He has time in His hand. No time passes over Him, through Him, under Him. Because He is eternal. Now, concerning the circle of the earth, it is written, in Job 26:10 (Look at the NASB Version, the Darby Version),
"He has inscribed a circle on the surface of the waters at the boundary of light and darkness."
and, in Proverbs 8:27,
"When He established the heavens, I was there, when He inscribed a circle on the face of the deep,"
These verses show that God created a circle around the earth. It is about this circle around the earth Isaiah speaks concerning the circle of the earth, as the circle that belong to the earth, around it. No matter of any sphere. Isaiah speaks about what this circle represents, its relation with the planet, not about the shape of the Earth. Now this circle means the Alpha and Omega, the eternity, the beginning and the end, as the beginning merges with the end in a circle. It is to be understood spiritually and, relatively, physically.