I thought they decorated the day after Thanksgiving. I read that the parks transform like magic over night. The last time we went, we arrived on Thanksgiving evening and went straight to Epcot to eat. We only did a few things, but basically stayed near the Land and the attractions that were open over there. By the time we went to the parks the next day, it was all decorated!! But i just read somewhere that the past year or two, they start decorating the week before THanksgiving. So Im not sure which is right!!