OP, you said you are going over Thanksgiving but there are no parties the week of Thanksgiving. There is a party November 21, and the next one is November 30. The parks will be so crowded during the holiday that they do not close MK at 7 during that week.
I personally would not do a TS much later than 4:30. If you are not seated on time there is a chance you would be in a restaurant when the party starts. You are paying a premium for the party time and atmosphere, you really shouldn't miss any of it.
Also, if you are interested in the rare character meets like the Seven Dwarfs, the lines start forming around 5:30.
We usually do a TS lunch, go to MK at 4, and have a CS meal sometime before 7.
Main Street and the Hub are very crowded during the parties, I try to avoid those areas during Holiday Wishes and the parades. There is great parade viewing in Frontierland. Don't miss the parade, the toy soldiers are my favorite part!