The dbms_flashback package is one method used to enable flashback mode. The ENABLE_AT_TIME procedure enables flashback mode to the specified time. For flashback support, Oracle saves an SCN every five minutes. The time specified in the ENABLE_AT_TIME procedure is converted to the next lower SCN.
Only the current session is affected by flashback query mode. Database-wide support is not available. Users will need EXECUTE privilege on the dbms_flashback supplied package.

Supplemental Notes:
To change the flashback time, you must disable flashback mode and re-enable. See the DISABLE example later in this section.
Error “ORA-08180: no snapshot found based on specified time” if flashback time too old, I.e. an earlier time than any UNDO data exists for.
Error “ORA-01466: unable to read data - table definition has changed” returned if a table involved in the flashback operation (SELECT, INSERT) did not exist at the specified flashback time or was altered after the specified flashback time.
Error “ORA-08182: operation not supported while in Flashback mode” if DML is attempted while in flashback mode.