In dm_docbase_config, there is a field "r_normal_tz". The explanation in this document is:
Indicates the storage mode used for date values. 0 directs content server to store all date values in UTC time. A value other than 0 represents the time zone offset from UTC time used by content server to normalize all date values for storage. A Time Zone offset must be expressed as seconds. for example, if the offset is for PST (Pacific Standard Time), the value is greater than 28800 (larger 8*60*60 ). this defaults to 0 for a new 6.0 or later repository and to an offset representing the server local time for a repository that is upgraded from a pre release 6.0 release.
All Date and Time values will be stored as the UTC (Coordinated Universal Time) in new repositories. This value can be resetted using "r_normal_tz" attribute of the docbase config object.
all date and time values will be stored as the servers local time for the upgraded repositories. this value cannot ressetted for the upgraded repositories. because "r_normal_tz" attribute is set with the Offset Value of the Content Server local time and it cannot be changed.