I'd use diff to yield the file list directly, e.g:
git diff --name-only "@{3 days ago}" "@{2 days ago}"
changelog.txt
newfile.txt
In case you're curious which file got modified or added, use --name-status instead:
git diff --name-status "@{3 days ago}" "@{2 days ago}"
M changelog.txt
A newfile.txt
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