Date to seconds to date is not that complex:
Code:
SQL> SET ECHO ON VER OFF
SQL> ALTER SESSION SET NLS_DATE_FORMAT='YYYY-MM-DD HH24:MI:SS';

Session altered.

SQL> COL sec new_value sec
SQL> SELECT SYSDATE, TO_CHAR (SYSDATE, 'J') * 86400
  2                + TO_CHAR (SYSDATE, 'SSSSS') sec
  3    FROM DUAL;

SYSDATE                       SEC
------------------- -------------
2009-08-05 12:53:05  212116279985

SQL> SELECT &&sec sec,
  2           TO_DATE (TRUNC (&&sec / 86400), 'J')
  3        + ((&&sec - TRUNC (&&sec / 86400) * 86400) / 86400)
  4    FROM DUAL;

          SEC TO_DATE(TRUNC(21211
------------- -------------------
 212116279985 2009-08-05 12:53:05

SQL>