Specifies the date output format in keyword substitution, and specifies the  default  time  zone  for date  in  the  -ddate  option.   The zone should be empty, a numeric UTC offset, or the special  string LT  for  local time.  The default is an empty zone, which uses the traditional RCS format of UTC  without any time zone indication and with slashes separating the parts of the date; otherwise, times  are output  in  ISO  8601 format with time zone indication.  For example, if local time  is  January  11, 1990,  8pm  Pacific Standard Time, eight hours west of UTC, then the time is output as follows:

    option    time output
    -z        1990/01/12 04:00:00        (default)
    -zLT      1990-01-11 20:00:00-08
    -z+05:30  1990-01-12 09:30:00+05:30

The -z option does not affect dates stored  in  RCS files, which are always UTC.