On the calendar on Seaworld's website, look for any day in November and December that lists a park closing of 9:00pm or 11:00pm. Those will be the Christmas celebration Days/Nights. Any day in November that lists a 6:00pm closing will not have the Christmas celebration, but 6:00pm closings in December will still offer the Christmas themed attractions like Polar Express experience as well as Christmas decor but not the Christmas themed shows.
http://seaworldparks.com/en/seaworld-orlando/Park-Info/Park-Hours
So according to the Seaworld Calendar, the dates in November and December 2013 with closing times of 9:00pm and 11:00pm are....
Friday, November 23rd thru Sunday, December 1st
Friday, December 6th thru Sunday, December 8th
Friday, December 13th thru Tuesday, December 31st
So those dates above are most likely your dates for the Christmas celebration for 2013.
Note: This past year, the Christmas celebration extended into January. But park closing times for 2014 aren't listed yet. So as this year progresses, keep checking January 2014 on the calendar for park closing times.