I've asked this kind of question before and the only answer I ever found is that Disney won't publish when they're instituting peak dining charges. Nice, eh? I'm guessing that it will closely line up with the peak periods on the dining plan but I also figure that they'll charge the surcharge any time the restaurants fill up just because they can. I'm normally somewhat of a Disney appologist but this one just drives me nuts. For my February trip, I've budgetted as though we'll be charged the surcharge and if we're not then I'll consider that a bonus. Two of my five ADRs will be subject to it. I believe all fixed price restaurants are subject to the surcharge with the exception of those that are prepaid I believe (CRT, SoA, HDDR & MBYBBQ).
If I had to guess, I would think that surcharges would be in effect through 1/2 since that's the Sunday after new years and there will be a mass exodus from WDW on that day, but obviously that's pure speculation on my part.