Crowds are normally HUGE through New Year's Eve. The week between Christmas and New Year's is the busiest attendance week of the entire year. We normally arrive on Jan 1st or 2nd and crowds get lighter day by day. I expect this year to be pretty heavy right through the weekend of the 3rd and 4th. Most schools won't start back until January 5th with New Years Day falling on a Thursday.
On the good side, the parks have longer hours and the holiday decorations normally stay up through the first few days in January.