create table C_SLEEP_LOCK(Un) as select 1 from dual;

create or replace procedure C_sleep(seconds in number default 1) is

i number;

procedure sleep_on_rowlock is
pragma autonomous_transaction;
tmp number;
resource_busy exception;
pragma exception_init (resource_busy, -30006);
begin
select Un into tmp from C_SLEEP_LOCK for update wait 1;
exception
when resource_busy then null;
end;

begin

savepoint sleeper_savepoint;
select Un into i from C_SLEEP_LOCK for update;
for i in 1..seconds loop
sleep_on_rowlock;
end loop;
rollback to savepoint sleeper_savepoint;

end C_sleep;
/
You can now test:
Exec C_sleep(10); — 10 seconds (about) wait.

You can find the explanations there: http://blog.tanelpoder.com/2008/05/25/using-autonomous-transactions-for-sleeping/