The key repeat interval is the time period, in seconds and microseconds,
between key repeat events once the initial key repeat threshold has
elapsed. (See Setting the Key Repeat Threshold.)  Like the key
repeat threshold, this is normally issued by Intuition and preset by the
Preferences tool.

You set the key repeat interval by passing a timerequest with
IND_SETPERIOD set in io_Command and the number of seconds set in tv_secs
and the number of microseconds set in tv_micro. struct timerequest
*InputTime; /* Initialize with CreateExtIO() before using */

   InputTime->tr_time.tv_secs=0;
   InputTime->tr_time.tv_micro=12000;  /* .012 seconds */
   InputTime->tr_node.io_Command=IND_SETPERIOD;
   DoIO((struct IORequest *)InputTime);

The code above sets the key repeat interval to .012 seconds.

   The Right Tool For The Right Job.
   ---------------------------------
   As previously stated, you must use a timerequest structure with
   IND_SETTHRESH and IND_SETPERIOD.