http://webexhibits.org/daylightsaving/b.html

Beginning in 2007, most of the United States begins Daylight Saving Time at 2:00 a.m. on the second Sunday in March and reverts to standard time on the first Sunday in November. In the U.S., each time zone switches at a different time.

So for 2007, DST starts March 11 at 2am and ends Nov 4 at 2am.