Many here are a bit confused, so let's be plain about it: Jehovah's Witnesses do NOT believe in evolution of any form, simple as that.
They also plainly say NO to 'creationism' which teaches that God created the whole universe in six literal days, as it is not Biblical. In fact, the first two verses of Genesis state the circumstance that exist BEFORE those six days (even the earth existed before the first day). The first actually starts in verse 3 with the phrase "And God said" and that same phrase precedes every new day as creation unfolds. All six days are also declared with the same phrase that "God was it was good, an evening..." etc.
At the end of those six creative days, Genesis 2:4 says: "This is the account of the heavens and the earth when they were created, in the day that the LORD God made earth and heaven."
Interestingly, that day is in fact all the six days combined. Hence some translations with take the Hebrew word for "day" and use the word "time that God created...".
So "day" can also be equated to a period of "time" or even an "era" or epoch" - like, things were very different in my Great Grandfather's "day" when they did not have computers or the internet.
So here Genesis 2:4 is using "day" in a way that cannot be 24 hours. Also, Genesis uses the word "day" in Genesis 1:5 to signify "daylight hours" or 12 hours only.
So we now see THREE different usages in Genesis for the word "day".
BUT: Everybody forgets there were in fact seven days and not just six.
The "seventh day" was not a 24 hour rest that God had as if he was somehow tired. The rest simply meant that his creation activity came to a rest, or stop.
Why is that so significant?
Simply because the Apostle Paul in Hebrews 4 alerts us to the fact that this rest is ongoing and he actually says "that day remains" in verse 6 and that we can enter it too, but must put behind us our evil ways.
So clearly, if the seventh days is thousands of years old, hence so must the other six days be thousands of years each.
Seems that we are still in the "seventh day" right now - as wickedness has not come to an end. One day the "seventh day" will come to an end. Watch out as that means God's intervention will make it happen!
So the clarity of belief of Jehovah's Witnesses is stark. They absolutely believe in the Genesis Creation account in every respect.
Note that stark and clear position stands very separate to that of so-called creationism - and creationism is tantamount to wanting to squeeze God into a human timetable by insisting on six literal days.
Finally, no matter how long creation took place, does insisting on six literal days make creation any lesser or greater than it already is? Every atom, particle, photon or molecule will not have changed one iota. So please, can we put the nonsense of creationism behind us by saying "God created everything in his own time and that of nobody else's."