Diagnosing a performance issue

We had a performance problem where the application took 8 seconds instead of less than 1 seconds. I ran the command and the output is below. My question is why the explain plan says UPDATE took 1 second whereas the query against dba_hist_active_sess_history tells that update statement was the costliest in terms of time taken?

  1  select sql_id,count(*),event,sum(time_waited) from dba_hist_active_sess_history
  2  where sample_time between to_timestamp('01-JUL-14 09:19:00 AM') and to_timestamp('01-JUL-14 09:21:00 AM')
  3  group by sql_id, event
  4* order by 4 desc
DBA_USER  prod_dcop >/

SQL_ID          COUNT(*) EVENT                                                            SUM(TIME_WAITED)