l_start := sysdate;
while sysdate - l_start <  10  /  24 / 3600  loop
  null; -- или любая операция занимающая время
end loop;

declare
  l_start date;
  cntr number;
  dummy number;
begin
  l_start := sysdate;
  cntr :=  0 ;
  while sysdate - l_start <  10  /  24 / 3600  loop
    cntr := cntr +  1 ;
  end loop;
  dbms_output.put_line('Iterations with NULL: ' || cntr);
  l_start := sysdate;
  cntr :=  0 ;
  while sysdate - l_start <  10  /  24 / 3600  loop
    dummy := sin(cos(tan(cntr)));
    cntr := cntr +  1 ;
  end loop;
  dbms_output.put_line('Iterations with OPs: ' || cntr);
end;

Iterations with NULL:  135315 
Iterations with OPs:  8023 

create or replace
procedure my_sleep( p_sleep in number )
as language java
name 'java.lang.Thread.sleep( long )';
/

SQL> begin
   2     my_sleep( 5000 );
   3   end;
   4   /

PL/SQL procedure successfully completed.

Elapsed:  00 : 00 : 05 . 00