Short Answer: Black Friday
Long Answer:
I have read that Super Bowl Weekend is the best time to buy a T.V. (best as in cheapest). I doubt though that they took into consideration Black Friday since the best deals are in very limited quantities, and you have to camp for them overnight.
I'm assuming that they took the prices of all the weekly general sales and found that the week of the Super Bowl has the lowest prices.
So if you want time to hem and haw and compare, or want a tv not being used as a door buster, or just don't want to deal with insane crowds, you might consider Super Bowl weekend. Otherwise you should be looking to get a T.V. on B.F.