This kit updates/etc/zoneinfo time zone data files to incorporate the most recent changes in various time zones around the world, most notably the US Daylight Savings Time (DST) rule changes that were passed into law on August 8, 2005 and take effect in 2007.
That law moves the start of DST from the first Sunday of April to the second Sunday of March. It moves the return to Standard Time from the last Sunday of October to the first Sunday of November. These changes affect all US time zones and a number of other North American time zones in other countries as well.