We sent last year during this time period. We usually go over Thanksgiving and the week after, but purchased Season Passes the year prior and had to go earlier than we did the year before.
It was the least crowded I have ever seen in WDW until about The Thursday prior to Thanksgiving.
There was one night in Epcot where the Countries were literally almost empty!! We had never experienced that before, even going the week after Thanksgiving.
The parks do close earlier, but they also do during the week of Thanksgiving, except for the couple days that the park is VERY VERY busy!
The difference is, you see less even though the park is open later because the crowds are huge. Go to early entry and take advantage of fast passes and you should be able to see a lot because the crowds are very manageable.
This time of year it's usually the following:
AK - 5pm
MK - 6pm
MGM 7pm
EPCOT - 9pm
I find that it's best to plan dinner after the park closes so you save time there. We find when the parks are open later we eat dinner anyway prior to the park closing so we really end up stopping around the same time anyway.