/sys$common/syshlp/helplib.hlb SET, OUTPUT_RATE, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 delta-time

    The time interval at which output is written from the output
    buffer to the batch job log file. If no delta time is specified,
    the information is written in the output buffer to the log file,
    but the output rate is not changed from the default of once per
    minute. Specify delta-time as [dddd-][hh:mm:ss.cc]. For more
    information on delta time, refer to the OpenVMS User's Manual or
    the online help topic DCL_Tips (subtopic Date_Time).