This change is the first in the US since 1987. From 1987 through 2006 DST extended from the first Sunday in April (April 2, 2006) to the last Sunday in October (October 29, 2006).
As has been the case, the time change occurs at 2:00 am in each time zone. This creates a one-hour period of ambiguity in the fall, because of overlap, e.g., 1:30 am occurs twice on November 4, 2007, locally first on the MDT clock then one hour later on the reset MST clock. A related issue is the fact that the one-hour period 2 am-3 am never occurs on the date of the transition from standard to daylight saving time, e.g., on March 11, 2007. Thus the dates of the standard time to daylight saving time transition are 23 hours in length and the dates of the daylight saving to standard time transitions are 25 hours in length.