Hi, There are some mistakes in the rules of PRC. The start and end time of DST in China should be 2:00 (i.e. 2:00 to 3:00 at the start and 2:00 to 1:00 at the end). Also in 1988, the start date should be 17 May instead of 10 May. Government notices about summer time: 1986-04-12 http://www.zj.gov.cn/attach/zfgb/198608.pdf p.21-22 (To establish summer time from 1986. On 4 May, set the clocks ahead one hour at 2 am. On 14 September, set the clocks backward one hour at 2 am.) 1987-02-15 http://www.gov.cn/gongbao/shuju/1987/gwyb198703.pdf p.114 (Summer time in 1987 to start from 12 April until 13 September) 1987-09-09 http://www.gov.cn/gongbao/shuju/1987/gwyb198721.pdf p.709 (From 1988, summer time to start from 2 am of the first Sunday of mid-April until 2 am of the first Sunday of mid-September) 1992-03-03 http://www.gov.cn/gongbao/shuju/1992/gwyb199205.pdf p.152 (To suspend summer time from 1992) The first page of People's Daily on 12 April 1988 stating that summer time to begin on 17 April. http://data.people.com.cn/pic/101p/1988/04/1988041201.jpg Proposed rules: Rule PRC 1986 only - May 4 2:00 1:00 D Rule PRC 1986 1991 - Sep Sun>=11 2:00 0 S Rule PRC 1987 1991 - Apr Sun>=11 2:00 1:00 D Regards, P Chan