The reason God created this heaven and earth in 7 days is to foreshadow how long it will last for, which is 7,000 years. The last 1,000 years correspond to a Sabbath rest for the entire earth, which in Hebrews is spoken of,
And this is what is also spoken of as the "millennial kingdom",
The earth is currently approximately almost 6,000 thousand years. You may even look at the Jewish calendar to see this, which is an estimate of years since the beginning of creation.
There remains, then, a Sabbath-rest for the people of God; (Hebrews 4:9 [NIV])
Blessed and holy are those who share in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years. (Revelation 20:6 [NIV])