Eastern Daylight Saving Time was not in use on the 21st of December 2010 (unless you are referring to Australian Eastern Daylight Saving Time). Even if it were, you would need to specify a city or a set of geographical coordinates.
The sunset time on December 21, 2010, Eastern Daylight Time was approximately around 4:32 PM.
The exact sunrise/sunset times varies from city to city.
The times for New York City on 23-May-2010 is; Sunrise 4:23 am. Sunset 7:20 pm
8:34 PM Eastern Daylight Saving Time
around 8 PM Eastern Daylight Saving Time
7:30 PM Eastern Daylight Saving Time
8:25 PM Eastern Daylight Saving Time
7:54 PM Eastern Daylight Saving Time
8:15 PM Eastern Daylight Saving Time
Sunset time on May 12, 2012, in St. Augustine, FL was around 8:00 PM Eastern Time.
between 8:50 and 9 PM Eastern Daylight Saving Time
Sunset at Shepherdstown, West Virginia on 22 September 2012 is at 7:07 PM Eastern Daylight Saving Time.
Sunset on October 13, 2012 in Rocklin, California was at approximately 6:29 PM PDT.
6:48 PM Central Daylight Saving Time
Sunset at Rawlins on 23 April 2011 was at 7:58 PM Mountain Daylight Saving Time.