So according to WT/JW chronology , the earth /universe could have been created millions of years ago However they say , ,Adam was created approximately 6000 years ago
Russell and early WT doctrine said that the entire creation process was 7,000 years per creative day, making the earth less than 50,000 years old. Old world Bible doctrine and belief. However, science has proven the earth (and universe) is much older, so the WTS has had to tweak their doctrine to align with what is commonly called 'gap creationism'. The universe and earth came into being millions of years ago, but the 'creative days' began just a short time ago (thus the 7,000 year creative days). Everything on the earth was created during this time, including Adam 6,000 years ago.
Problem with that is that it does not agree with the Bible. Exodus 20:11 - 'For in six days the LORD made the heavens and the earth, the sea, and all that is them...'
The WTS has painted themselves into a corner with their 'gap creation' belief. It agrees with neither science nor the Bible.