Example in alert.log:

Tue Oct 12 08:14:18 2010
ORA-01555 caused by SQL statement below (SQL ID: f8ry9dcxgdr6z, Query Duration=1286871258 sec, SCN: 0x0000.06a688b7):
Tue Oct 12 08:14:18 2010
select...

Here query duration is 1286872197 sec, that is 40 years. Clearly not accurate.

But we know that the cursor SCN is 06a688b7 in hexa, so:

SQL> select scn_to_timestamp(to_number('06a688b7','xxxxxxxx')) from dual;

SCN_TO_TIMESTAMP(TO_NUMBER('06A688B7','XXXXXXXX'))
---------------------------------------------------------------------------
12-OCT-10 07.57.31.000000000 AM

Query has failed at 08:14 when trying to get a consistent read as of 07:57, so the query duration was 16 minutes.