The WT Society has modified their understanding of the Creative day. The Creation Book(1985) brings out this interesting point:
The first part of Genesis indicates that the earth could have existed for billions of years before the first Genesis "day," though it does not say for how long. However, it does describe what earth’s condition was just before that first "day" began: "Now the earth proved to be formless and waste and there was darkness upon the surface of the watery deep; and God’s active force was moving to and fro over the surface of the waters."—Genesis 1:2.
Although this publication states that they can't be sure how long a Creative day existed, and whether the next Creative was greater or less than one another. They relate that the Creation account just provides a succesion of what took place after each other.
The concept of a Creative day being 1,000 years old was an older understanding, and eventually was replaced as more realistic evidence became available to support this understanding. The Society should have left things alone when they couldn't determine just how long a Creative day was. However, it's a mistake that was finally corrected.