The genealogy to Christ from Adam begins
after Adam and Eve were no longer inside the Garden of Eden with God, Who is eternal, and not limited by time. The timeline estimate on that geneology counts that time starting from Adam and Eve no longer in the Garden, and assuming the genealogy has no gaps (there is more than one available in scripture) until Christ.
But we do not know from the Bible how long they were in the Garden. With the Eternal One for Whom time is so little a thing, and with the Tree of Life in the Garden....
How much time passed in the external world of Earth while they walked in the Garden with God?
We do not know.
It could have been some vast stretch of time for all we know.
That's biblically consistent -- that it could have been any particular length of time.
Also, biblically, we do not know how much time passed during verse 1 of Genesis 1:1 before the moment later in verse 2:
1 In the beginning God created the heavens and the earth.
2 Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.
The heavens are the entire universe, and we do not know how much time passed, biblically, during verse 1, before the moment in verse 2.
It could have been a vast stretch of time.
Adding assumptions
not in the Bible a person could say or think or assert it was a short time.
But the Bible does not say that.
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Resource: The Bible without added assumptions it does not say.