Very Computer

For example, if the session has completed and there are three SQL statements
that waited for 10,5 and 50 seconds respectively the total wait time would
be 65 seconds.

The name of the wait may vary slightly with version,
but look at v$session_event for 'enqueue' waits.  You
will need to have timed_statistics = true to get times.
You may also (depending on application) want to
look at something with a name like 'PL/SQL sleep waits'.

Best bet:
    connect as SYS

    create or replace view v$my_session_event
    as
    select * from v$session_event
    where sid in (
            select sid from v$session
           where audsid = userenv('sessionid')
    );

    grant select on v$my_session_event to public;
    create public synonym v$my_session_event;

--

Jonathan Lewis
Yet another Oracle-related web site:  http://www.jlcomp.demon.co.uk