REM Output will list out all the session that are idle for more than 1 hr.
REM last_call_et is in seconds .You can give where clause accordingly.
REM
REM Ex : for 2hrs:7200 etc.
REM
REM Once identified ,if you want to kill those session ,
REM you can use this command:
REM
REM alter system kill session '<sid>,<serial#>';

select sid,serial#,username,trunc
(last_call_et/3600,2)||' hr'
last_call_et
from V$session where
last_call_et > 3600 and username is not null
/