Actually, this year, you have until January 4th. The dealers don't want to lose out on the weekend, so they are keeping year end specials available all weekend, in many places. But, I wouldn't wait until Sunday to start playing the negotiation game.
I didn't need to buy my truck when I did, but the percentage I got off of MSRP was about what the deals were pre-Covid, so I didn't think I'd do much better. By holding out, I might have saved another $1000, but I could've also lost all deals as inventory diminishes. I'm satisfied getting 19% off MSRP in early December