Our experience in the past is that when you start your trip prior to the date rates go up you get that rate the entire time. And, we have gotten great code rates by going a little early.
If you have flexibility in your dates, the week after Thanksgiving is great. The crowds are fewer at the parks and there are some very nice rates out there for all the resorts.
We arrive on Thanksgiving Day and have not yet been able to get a good rate for the first three days. But after that we have an excellent rate on a savannah at ALK.