tracefile tim to readable date format

In trace file, the time is recorded, this could be used to measure time between two timestamps But how do you convert 31796862227375 to a human format? This is how I proceeded : SQL> oradebug SETMYPID Statement processed. SQL> oradebug tracefile_name /u01/log/oracle/diag/rdbms/db01/DB01/trace/DB01_ora_32440740.trc SQL> alter session set   nls_date_format='YYYY-MM-DD_HH24:MI:SS'   sql_trace=true; Session altered. SQL> select '&_DATE','Start' from dual; […]