VMS Help System Services, $SETIME, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 timadr

    OpenVMS usage:date_time
    type:         quadword (unsigned)
    access:       read only
    mechanism:    by 32- or 64-bit reference (Alpha)
    mechanism:    by 32-bit reference (VAX)
    New absolute time value for the system time, specifying the
    number of 100-nanosecond intervals since 00:00 o'clock, November
    17, 1858. The timadr argument is the 32-bit address (on VAX
    systems) or the 32- or 64-bit address (on Alpha systems) of a
    quadword containing the new system time value. A negative (delta)
    time value is invalid.

    If you do not specify the value of timadr or specify it as 0,
    $SETIME recalibrates the system time using the time-of-year
    clock.