Creating and Managing Timezone Definitions?
One issue with the UTC implementation on OpenVMS is the behaviour of C functions and other programs that use SYS$TIMEZONE_RULE; the OpenVMS mechanism assumes all control over the timezone and the daylight time switchover. This allows calculation of the time by the C library and various applications. 4-17 Time and Timekeeping This can be incompatible with a system or application that requires manual modifications to the DST or TDF settings, or that requires a local or customized timezone definition. For such a site to ensure the timekeeping is correct, the site must provide procedure that sets the local time and the TDF when the SYS$TIMEZONE_RULE says to do it. If a site requires a non-standard time switch-over, as in coordinating with a shift change or due to changes in the local or regional timezone rules, the site will need to use the zic compiler to create a custom timezone rule. Additionally, applications may need to have special actions taken or actions queued just before the time
