It is true that the Watchtower were not the first to come up with the 7,000 year creation-day theory, but they were the most strident and held on to the teaching for several years. They have never formally retracted the teaching, but have made more cautionary statements over the years. For instance, the original "[Human] Reasoning on the Scriptures" book accepted this teaching, but the revised edition, published in 1989 merely mentions the time as being "several thousand years in length".
As other posters have mentioned, the Watchtower no longer makes any reference to this teaching, which they once held with such passionate vigour. Basically, the "[human] reasoning" behind this teaching was:
1. Every one one of the six creative days are said to begin and end, using the Hebraic expression, the "evening and the morning was....". But no such expression is used with the seventh day. Therefore the only "reasonable" conclusion is that the seventh day did not end during the time of the Bible record.
[Answer: Most Evangelical Christians will disagree. This is not the only "reasonable" conclusion to draw. Because the seventh day was to be a day of special significance in Jewish theological perception, its end was not signified by the expression common to the other days. Its end was signified by the expression "And God rested on the seventh day...". Despite the convoluted way Franz "translated" this phrase implying a present continuous structure, the Hebrew perfect as used here is a past tense, hence a completed action, not a continuing one.]
2. The Seventh day must be still continuing because Hebs:4:4-6 speaks of Gods "rest day" being in operation at this time.
[Answer: Again Evangelicals will disagree. This is not talking of the Seventh creation "day" - since "day" is not used here. It is talking of God's Rest, not His rest "day". The writer of Hebrews is discussing how we enjoy security or rest by believing in Christ. God's rest, since Calvary has been to gather believers in Christ who can have the security of belief and freedom from the fear of death. They do this by entering God's rest. This is contrasted with the Exodus generation who lacked such belief.]
3. Since we "know" that Adam was created in in 4026 BC, more than six thousand years of human history has passed. [6037 years to be precise] So we must be periously close to the end. It is necessary then to accept the GB and all its pronouncements and hasten to join the Organization to survive into the New World.
[Answer: There is no answer. Since 1889, when the Watchtower first published a date for Adam's creation, [4128 BC] it has had the need to correct this date five further times:
1.1896: 4129.
2.1943: 4028
3.1944: 4026
4.1953: 4025
5. 1963: 4026]