From AWAKE! Oct 8, 1966 pp. 19-20}
"'How Much Longer Will It Be?' 6,000 Years Completed in 1975 .. In what year, then, would the first 6,000 years of man's existence and also the first 6,000 years of God's rest day come to an end? The year 1975.. Hence, the fact that we are nearing the end of the first 6,000 years of man's existence is of great significance. Does God's rest day parallel the time man has been on earth since his creation? Apparently so. From the most reliable investigations of Bible chronology, harmonizing with many accepted dates of secular history, we find that Adam was created in the autumn of the year 4026 B.C.E. Sometime in that same year Eve could well have been created, directly after which God's rest day commenced .. There is another chronological indication that we are rapidly nearing the closing time for this wicked system of things. It is the fact that shortly, according to reliable Bible chronology, 6,000 years of human history will come to an end.. After six thousand years of toil and bondage to sin, sickness, death and Satan, mankind is due to enjoy a rest and is in dire need of a rest. (Heb. 4:1-11) Hence, the fact that we are nearing the end of the first 6,000 years of man's existence is of great significance.. In what year, then, would the first 6,000 years of man's existence and also the first 6,000 years of God's rest day come to an end? The year 1975. This is worthy of notice, particularly in view of the fact that the 'last days' began in 1914, and that the physical facts of our day in fulfillment of prophecy mark this as the last generation of this wicked world. So we can expect the immediate future to be filled with thrilling events for those who rest their faith in God and his promises. It means that within relatively few years we will witness the fulfillment of the remaining prophecies that have to do with the 'time of the end.'"
There are many, many references to 1975 in WTBTS literature.