As was pointed out, the Watchtower wants to avoid problems with "the world" and with old-time JWs brought up on the notion of 7000-year creative days. So they fudge and instead of giving a definite time period, like they used to, they use vague words like "millennia" and "thousands of years". This is consistent with the old-timers' belief of 7000-year days, and with modern geological dating since a billion years certainly can be described as "millennia". The former doesn't raise questions with the old-timers about the Society's veracity, so it's a Good Thing. The latter is stupid, of course, because it's like giving your age in microseconds, but avoids JWs having to try to convince prospective JWs of the ridiculous notion that life has only been on the earth for a couple of tens of thousands of years. So by being vague, the Society kills two birds with one stone.
For some years I've attempted to get various JWs I've come in contact with to give me a straight answer about the 7000-year creative day notion. A few, who I already knew were way out in left field JW-wise, admitted that the notion is in limbo. Several rank-&-file JWs promised to get back to me with an answer but never did. Several Watchtower officials absolutely refused to give a straight answer, simply dancing around it. So it's obvious to me that the Society has in place an explicit policy -- given, of course, only to WTS officials -- to avoid answering that question. The reason they do this is obvious: they want to avoid unanswerable criticism from knowledgeable "worldlings" and they want to avoid alienating long-time JWs who still believe in the 7000-year notion.
Bonnie_Clyde mentioned a Jan. 22 Awake! article about a man who got a Ph.D. in physics and simultaneously became a JW, who claimed that "one of the things that convinced him it was truth was that the Bible teaches that the creative days were "thousands" of years long--not 24 hours." This article was obviously highly massaged by the Watchtower editor to make the guy's "recollections" be in line with "present truth". No one working on a Ph.D. in physics in the 1970s could possibly be so stupid as to accept that macroscopic animal life has been on the earth for only 20,000 years -- which is exactly what the Watchtower was teaching at that time.
As for Genesis itself, if one insists on a literal interpretation of "day", then one might as well throw it in the garbage, since life is provably several billion years old, and life with nicely fossilizable hard parts (such as is preserved from the so-called "Cambrian explosion") is at least half a billion years old. So Christians who want to maintain the idea that the entire Bible is accurate, and in particular accurate where science is concerned, have no choice but to interpret the Hebrew "yom" in Genesis in a more general way than as a literal 24-hour time period. I see no particular problem with that.
Genesis does have problems, though, with the order in which creation is presented (I can accept that certain oddities, such as the statement that the sun and moon were "made" well after light appeared, refer to the viewpoint of someone on the surface of the earth). For example, Gen. 1:11 states that fruit trees were created on the third day, before animal life was created on the fifth day, but the fossil evidence proves that fruit trees appeared about 120 million years ago, some 400 million years after the "Cambrian explosion" of animal life. Gen. 1:20-25 states that all of the "flying creatures" (which for the Hebrews who recorded Genesis included birds) were created before any of the land animals (which includes amphibians, reptiles and so forth), whereas the fossil record indicates that flying creatures appeared long after the first land animals -- whether you talk about insects, flying reptiles, birds or bats. So for a Christian to claim that Genesis has any validity at all, he must claim that the order of creation presented in Genesis is at best allegorical (or whatever term one likes that means "not to be taken literally").
As for predictions about "the end" by the Watchtower or anyone else, based on "bible chronology", it's pretty obvious that according to the Bible itself, this is a fruitless endeavor. Jesus and the angels were directly involved in creation and knew the time periods involved. Yet Jesus explicitly stated that neither he nor "the angels in heaven" knew "the day or the hour", which is obviously a standard phrase meaning that they had no idea of the time period at all. If these intelligent creatures couldn't know the time of "the end", with their certain knowledge of events in time, then it's obviously impossible for humans to know either, no matter what they claim to pick out of the Bible. Why people who claim to be so knowledgeable of the Bible, such a JWs, don't understand this simple point, is a measure of their spiritual stupidity and willingness to be led down a garden path by false prophets.
AlanF