The most recent cumulative time zone update is available for download now. The KB2570791 was published on August 9th of 2011. The KB will be available on Windows Update on August 23rd of 2011.
This update is part of the regular cadence for publishing DST rules and Time Zone updates twice a year (fall and winter) as needed. Microsoft policy in response to DST and Time zone requests can be found here.
This update supersedes and replaces update 2443685 which was released in December of 2010. This update also includes additional time zones changes released as hotfixes after update 2443685 was published like the hotfix 2543367 that was published in April with changes for customers located in Chile, Egypt and Morocco.
Customers in Chile that applied hotfix 2543367 or apply the cumulative update 2570791 will be prepared for the upcoming start of the DST period on August 20th of 2011.
Based on the information published by Chilean government here the start of the DST period in 2011 will follow the rules below:
Start of the DST Period:
For the mainland and Chilean Antarctica the Daylight saving time starts: 24:00 of the third Saturday of August the clocks should go forward to 01:00 of the next day. For the DST period of 2011-2012 the new Start date is now August 20th, 2011.
For the Easter Island and Salas y Gómez Island the Daylight saving time ends: 22:00 of the third Saturday of August the clocks should go forward to 23:00 of the same day. For the DST period of 2011-2012 the new Start date is now August 20th, 2011.
For more information see Microsoft Knowledge Base: 2570791 August 2011 cumulative time zone update for Windows operating systems.