Before the year 1975 The Watchtower Society taught that Adam and Eve were created in the same year 4026 B.C.E. and right away ‘God’s rest’ began, so that the seventh day started, which will last 7,000 years. From that moment one should count 6,000 years which ended in 1975. Later, when the expected year passed, that view was changed, namely that it is unknown when God started to rest after creation of the first couple.
The following are several statements of The Watchtower Society concerning God’s rest right after the creation of Adam and Eve in 4026 B.C.E.
At the first let us mention that before 1975 campaign Jehovah’s Witnesses several times changed their mind on the above subject. For example a book published in 1953 taught:
The Christian era is now nearing its close and we are almost six thousand years from man's creation, after which God's resting began, or his desisting from earthly creation; and now the thousand-year reign of Jesus Christ is before mankind, after which he will hand over all things to God his Father. So, not by human interpretation, but by God's own interpretation, the seventh day of rest adds up to seven thousand years. (New Heavens and New Earth 1953, pp. 41-42).
Also another publication of that period stated:
The coming thousand-year period is the seventh thousand-year period since man’s creation, hence the final thousand years of Jehovah’s great sabbath day. (The Watchtower April 1, 1954, p. 222).
As we see, The Watchtower Society used to teach that God’s rest began right after man’s creation.
Later, a book published in 1963 taught something different (!):
The first edition of this book, published in 1963, stated: “Does this mean, then, that by 1963 we had progressed 5,988 years into the ‘day’ on which Jehovah ‘has been resting from all his work’? (Gen. 2:3) No, for the creation of Adam does not correspond with the beginning of Jehovah’s rest day. Following Adam’s creation, and still within the sixth creative day, Jehovah appears to have been forming further animal and bird creations. Also, he had Adam name the animals, which would take some time, and he proceeded to create Eve. (Gen. 2:18-22; see also NW, 1953 Ed., footnote on vs. 19) Whatever time elapsed between Adam’s creation and the end of the ‘sixth day’ must be subtracted from the 5,988 years in order to give the actual length of time from the beginning of the ‘seventh day’ until . It does no good to use Bible chronology for speculating on dates that are still future in the stream of time. - Matt. 24:36.” (“All Scripture Is Inspired of God and Beneficial” 1990, pp. 286-287 [see ed. 1963, pp. 285-286]).
So we see from the quotation that The Watchtower Society changed its view on God’s rest and later ceased to call people to avoid speculating on Bible chronology.
Afterwards, just before 1975 campaign, their view was changed again (!) in a book printed in 1965:
Because, after Jehovah God created Adam and Eve, his sixth creative day ended and his seventh day of desisting from earthly creative work began, which day he blessed and made sacred. (“Things in Which It Is Impossible for God to Lie” 1965, p. 303);
For the man that has entered into God’s rest has also himself rested from his own works, just as God did from his own [in 4026 B.C.E.] (“Things in Which It Is Impossible for God to Lie” 1965, p. 297).
The above view was supported by other Watchtower publications published during 1975 campaign, in the years 1966-1975. Notice the growing certainty concerning the discussed event. Here are some passages:
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. 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. (Awake! October 8, 1966, p. 19);
Does it mean that God’s rest day began 4026 B.C.E.? It could have. The Life Everlasting book does not say it did not. The book merely presents the chronology. You can accept it or reject it. If that is the case, what does that mean to us? [He went into some length showing the feasibility of the 4026 B.C.E. date as being the beginning of God’s rest day.] (The Watchtower October 15, 1966, p. 631);
According to the Bible timetable, man’s history on earth has been nearly 6,000 years. Adam was created in 4026 B.C.E., which means that six thousand years of human history end about the fall of 1975 C.E. We are in the great 7,000-year rest day of God, starting at the time he rested after the creation of Adam and Eve. There are, therefore, a thousand years left to run. Without Satan and his demons to disturb mankind it will indeed be a restful time. (The Watchtower July 15, 1967, pp. 446-447);
Since it was also Jehovah’s purpose for man to multiply and fill the earth, it is logical that he would create Eve soon after Adam, perhaps just a few weeks or months later in the same year, 4026 B.C.E. After her creation, God’s rest day, the seventh period, immediately followed. Therefore, God’s seventh day and the time man has been on earth apparently run parallel. (The Watchtower May 1, 1968, p. 271);
And yet the end of that sixth creative “day” could end within the same Gregorian calendar year of Adam’s creation. It may involve only a difference of weeks or months, not years. (...) After the sixth creative day ends, the seventh one begins. This time between Adam’s creation and the beginning of the seventh day, the day of rest, let it be noted, need not have been a long time. It could have been a rather short one. The naming of the animals by Adam, and his discovery that there was no complement for himself, required no great length of time. The animals were in subjection to Adam; they were peaceful; they came under God’s leading; they were not needing to be chased down and caught. It took Noah only seven days to get the same kinds of animals, male and female, into the Ark. (Gen. 7:1-4) Eve’s creation was quickly accomplished, ‘while Adam was sleeping.’ (Gen. 2:21) So the lapse of time between Adam’s creation and the end of the sixth creative day, though unknown, was a comparatively short period of time. (The Watchtower August 15, 1968, pp. 499-500);
“EVENING” OF SEVENTH CREATIVE “DAY” BEGINS, 4026 B.C.E. (God’s ‘Eternal Purpose’ Now Triumphing for Man’s Good 1974, p. 51).
After 1975 The Watchtower Society changed its view on God’s rest and returned to the view taught in 1963. Interestingly, that only after September 1975 it stated: “so it does us no good to speculate”. Here is the ‘new’ teaching:
It shows a time lapse between the creation of Adam and that of his wife, Eve. During that time, God had Adam name the animals. Whether that period amounted to weeks or months or years, we do not know. So we do not know exactly when Jehovah’s great “rest day” began, nor do we know exactly when it will end. The same applies to the beginning of Christ’s millennial reign. The Bible provides us no way to fix the date, and so it does us no good to speculate when that date may be. (The Watchtower October 1, 1975, p. 579);
Why do we not know when God’s “rest day” began and when it will end? Although the time of Adam’s creation can be determined, the beginning of God’s “rest day” cannot. This is so because there was a time lapse of unspecified length between Adam’s creation and the creation of Eve. Not until after the creation of Eve did God’s “rest day” begin. The start of that day being unknown, its end is likewise unknown. (The Watchtower January 1, 1976, p. 30);
For one thing, even though Bible chronology clearly indicates that we have reached the mark of six thousand years since the time of the creation of the first human, Adam, it does not tell us just how long after that event the sixth creative day came to its close and the seventh creative period or “day,” God’s great rest day, began. (...) But that great rest day did not begin immediately after Adam’s creation. (The Watchtower July 15, 1976, p. 436);
What, then, does this mean? Simply this: That these factors, and the possibilities for which they allow, prevent us from saying with any positiveness how much time elapsed between Adam’s creation and that of the first woman. We do not know whether it was a brief time such as a month or a few months, a year or even more. But whatever time elapsed would have to be added to the time that has passed since Adam’s creation in order for us to know how far along we are within God’s seventh “day,” his grand day of rest. So our having advanced six thousand years from the start of human existence is one thing. Advancing six thousand years into God’s seventh creative “day” is quite another. And we do not know just how far along in the stream of time we are in this regard. (The Watchtower July 15, 1976, p. 437).
We should also mention that the concept of 7,000 years (a span of each creative day) was abandoned by The Watchtower Society after a dozen or so years after 1975. Jehovah’s Witnesses organization taught about „God’s” and Biblical origin of that concept till 1987:
The Scriptures, together with subsequent facts which are indisputable proofs beyond a doubt, indicate that the seventh day or epoch of creation, mentioned in Genesis, covers a period of seven thousand years of our time (Creation 1927 p. 28);
So, not by human interpretation, but by God's own interpretation, the seventh day of rest adds up to seven thousand years. (New Heavens and New Earth 1953 p. 42);
The Bible record, together with verifiable history, indicates that the seventh day of that creative week covers a period of 7,000 years. Hence, each of the six preceding “days” would be of the same length. (Awake! November 8, 1982 p. 7).
Here are the last two texts about the period of 7,000 years:
Second, a study of the fulfillment of Bible prophecy and of our location in the stream of time strongly indicate that each of the creative days (Genesis, chapter 1) is 7,000 years long. It is understood that Christ’s reign of a thousand years will bring to a close God’s 7,000-year ‘rest day,’ the last ‘day’ of the creative week. (Revelation 20:6; Genesis 2:2, 3) Based on this reasoning, the entire creative week would be 49,000 years long. (The Watchtower January 1, 1987, p. 30);
nor will Jehovah bring forth new material productions during the present 7,000-year day of resting from his works of creation. (The Watchtower March 1, 1987, p. 27).
After 1987 texts about “thousands of years” for each creative day started to appear in The Watchtower Society’s publications. This change from “7,000 years” to “thousands of years” was possibly made under influence of rank and file Witnesses who could not find such a concrete number in the Bible and maybe they asked the organization for explanation. Here are some examples of that new concept:
This makes it evident that each creative day, or work period, was at least thousands of years in length. (Insight on the Scriptures 1988 vol. 1, p. 594);
A dazzling vision of God’s purpose accomplished, the preparations for which he had made by six creative days of work over thousands of years of time! (The Watchtower August 1, 1989 p. 27);
The first chapter of Genesis provides a completely reasonable account of how these “unrepeatable” “unique events” came about during creative ‘days’ that stretched through millenniums of time. (Bible - God’s Word or Man’s? 1989 p. 110).
Rejection of “7,000 years” was a covering up of the last trace connected to the year 1975 and the period 6,000 years along with the millennium which were to complement that period. According to the present teaching of The Watchtower Society, the expected millennial reign of Christ is not directly connected with the date of Adam’s creation in 4026 B.C.E. and with the beginning of God’s rest.