To be clear, you are right, they do not claim to know exactly how long the creative days were (as they once did). Since the 1990s they have used words like "indefinite" and "unknown" to describe them. However, at precisely the same time, in other articles, they use the more limiting expression "thousands" of years.
"Indefinite" or "unknown" does not contradict "thousands" of years. Most importantly it does not contradict the notion of approximately 7000 years, as indicated last in 1998.
JWs should be called to account for their real beliefs - even the ones they are trying to hide behind vague language.