To be fair, the Witness beliefs in this area have changed over time... one might say they evolved into something less likely to reduce people to hysterical laughter... but this means it is easy for ex-Witnesses and non Witnesses (as well as Witnesses) to be none-too-clear on what they do believe.
I think they started off on a "If 1975 = 6,000 years since Adam and the Millenium (1,000 years) is coming, the the last cretaive day = 7,000 years so all creative days = 7,000 years so "Let there be light" was (6,000+7,000x6) 48,000 years ago in 1975.
They jumped on the Old-Earth-Creationist band wagon of claiming "In the begining God created the Heavens and the Earth" bit was BEFORE the first creative day, so thus claimed the Universe was as old as anyone cared to say it was, but that the forming of the Earth and creation of everything was all within the last 50,000 years.
The blue 'Creation' in the mid 80's changed the "Creative day = 7,000 years" into "Creative day = epoch". I would have got out of the Borg in my teens if that hadn;t happened, but I was ignorant enough of science for that change to satisfy my disquiet over the obviously errant rubbish of 7,ooo year creative days.
However, JW's are frequently conditoned to jump like a scalded cat when anyone mentions any date with lots of zeros on it, so often, being surpirsingly ill-informed about what they do actually believe themselves, will have a knee-jerk reaction and argue against things that are actually permissable to believe in.
My mum did this the other day when I described Lot as a bronze-age pastoralist.