It clearly says the seventh day would begin in the fall of 1975:
According to this trustworthy Bbile chronology six thousand years from man's creation will end in 1975, and the seventh period of a thousand years of human history will begin in the fall of 1975 C.E.
Now really what is so hard to understand about that? It says nothing about a gap between when Adam was created and the beginning of the seventh day. The seventh day of 1000 years was to begin in the fall of 1975. If that day was to be IN the paradise then it couldn't start at a later date. Note also that is says "trustworthy Bible chronology" There is no maybe, or we hope, or perhaps about htis. If the 6th 1000-yr period was ending in 1975 then the seventh had to begin in 1975. There is no middle ground between the end of one day and the beginning of the next. JWs didn't jump ahead or blow their own expectations out of control. They saw it in black and white. And while the WTS selectively quotes only part of this sentence they, like always, omit the part that really matters
the seventh period of a thousand years of human history will begin in the fall of 1975 C.E.