NEW_TIME
NEW_TIME(x,time_zone1,time_zone2) converts x from time_zone1 to time_zone2.
The following query uses NEW_TIME() to convert date from PST to EST:
SQL> SELECT TO_CHAR(NEW_TIME(TO_DATE('25-MAY-2011 21:45',
2 'DD-MON-YYYY HH24:MI'), 'PST', 'EST'), 'DD-MON-YYYY HH24:MI')
3 FROM dual;
TO_CHAR(NEW_TIME(
-----------------
26-MAY-2011 00:45
SQL>