"DST will now start three weeks earlier and end one week later than in previous years as a result of the Energy Policy Act of 2005, which extended DST in the US to conserve energy. Beginning in 2007, DST will start at 2:00 a.m. on the second Sunday of March (instead of the first Sunday of April) and end at 2:00 a.m. on the first Sunday of November (instead of the last Sunday of October). This means that DST will begin on March 11, 2007 (instead of April 1, 2007) and end on November 4, 2007 (instead of October 28, 2007).

As usual, at the beginning of DST, one hour effectively disappears as 1:59 a.m. is followed by 3 a.m. At the end of DST, a duplicate hour appears as 1:59 a.m. is followed by 1:00 a.m., meaning that the 1:00 a.m. hour happens twice.

Because there are many types of medical devices and systems with clocks and clock-related features such as timers that were sold before the DST rule changes, e.g. they were designed with the old start and end DST dates, it is unknown whether these devices and systems will operate correctly with the new 2007 DST start and end dates.

Internal clocks in devices and systems usually change automatically for DST based on values set internally or interactions with other devices, e.g., servers. Some devices and systems may rely on incorrect values for DST starting and ending dates if the device manufacturers have not patched or fixed their devices to use the new dates"[1]