So, in summery, based on what I’ve seen:
FACT: JWs have always taught that "day" seven can be used to infer the length of the other days. This has been explicitly stated as recent as 1998 (see Creator Book, quoted above). Nothing has been published that contradicts or revises this teaching.
FACT: If the "end" comes as soon as JWs say it will, "day" seven will end up being about 7000 years long.
FACT: All six creative days are described as encompasing "thousands" of years each. The only reason for this slightly vague choice of words is that JWs cannot pinpoint the date of the beginning of “day” seven (something they once tried to do: 1975 fiasco) and therefore cannot know exactly how long it will end up being.
FACT: Neither the expression "billions of years" nor "millions of years" has ever been applied to the creative days. Both expressions, however, are routinely applied to the age of the universe and "formless" Earth.
FACT: "Billions of years" and "millions of years" are frequently used to describe the "false" teachings of science: evolution, geologic time scale, geologic column, etc...
CONCLUSION: JWs actually teach that each creative "day" was something like 7000 years long.
Based on JW literature, both past and preasent, I don't think it is possible to come to any other conclusion. And, I'm not even sure JWs are trying to hide it.