Initializing INTERVAL data type

Question

I have a situation in which I want to keep track of the amount of time it takes to perform a task that it comprised of a number of steps. I need to get the amount of time to perform each task by subtracting the stop and start times; then these need to be added to a running total to track the total time to perform the task. My PL/SQL code looks something like this:DECLARE
  start TIMESTAMP;
  stop TIMESTAMP;
  task_time INTERVAL DAY TO SECOND;
  total_time INTERVAL DAY TO SECOND;
BEGIN
  total_time := <an initial value (0)>;      -- How is this done?
  FOR i IN 1 .. <some upper limit> LOOP
    start := <some date and time>;
    stop := <some other date and time later than start>;
    task_time := stop - start;    -- Subtracting TIMESTAMPs results in an INTERVAL data type
    total_time := total_time + task_time;    -- Adding two INTERVALS results in an INTERVAL data type
  END LOOP;
END;My question, as noted in the code is how do you initialize an INTERVAL data type?
I have tried "total_time := 0" but I get a compile error because the types are not compatible. I have also tried setting it to "TO_DATE('00:00','hh24:mi')" but this also results in a type compatibility issue.
Should I be approaching the problem in another way completely?

Answer 1

Nothing could be simpler:
declare
v_interval interval day to second;
begin
v_interval := interval '0' hour;
dbms_output.put_line(v_interval);
end;