Syntax:

      /BEFORE = time-specification

  Use /BEFORE to specify the creation time of the oldest  history  list
  entry  you  want  to  save.   All  entries  made before that time are
  deleted.

  Time is specified as the  VAX  standard  time  of  day:   dd-mmm-yyyy
  hh:mm:ss.ss.   You  may  omit any of the fields, but you must include
  the punctuation (hyphen, colon, period) following any  leading  field
  you omit.  Omitted fields default to the current time of day.

  You cannot specify both /BEFORE and /KEEP in the same command line.