CREATE OR REPLACE FUNCTION on_time (DATE, TIME, DATE, TIME, INTEGER)
    RETURNS INTERVAL AS '
DECLARE
    ship_date   ALIAS FOR $1;
    ship_time   ALIAS FOR $2;
    curr_date   ALIAS FOR $3;
    curr_time   ALIAS FOR $4;
    miles       ALIAS FOR $5;
    appt_window INTERVAL;
    trav_window INTERVAL;
    func_name   TEXT DEFAULT ''on_time'';
    onTime      INTERVAL;
BEGIN

    appt_window = (ship_date + ship_time) - (curr_date + curr_time);
    trav_window = ''78 hours 17 minutes'';

    raise notice ''appt_window: %'', appt_window;
    raise notice ''trav_window: %'', trav_window;

    RETURN (appt_window - trav_window);

END;
' LANGUAGE 'plpgsql';