Day Difference is not working properly due to timezone conversion - postgresql

Question

I was working on a problem where we are creating a view. We have a task & the task has an estimated time put up by the creator, assigned_at, due_date. We need to distribute the estimated time b/w assigned_at to due_date. What I was doing is getting the days using the extract function and dividing the estimated time with days count. By default, we store timestamps as UTC. The days count not coming correctly.
Eg: A task has,
Due Date: 2022-03-24T18:30:00+00:00,
Assigned Date: 2022-03-23T20:09:57.028525+00:00,
Estimated Time: 10 //time to complete that task,
Per Day Estimated Time: 10(Estimated Time)/2 (No Of Days)=5
CREATE OR REPLACE FUNCTION public.get_task_estimated_time(start_date timestamp with time zone, end_date timestamp with time zone, total_estimate numeric)
RETURNS numeric
LANGUAGE plpgsql
AS $function$
declare
date_duration numeric;
begin
date_duration = extract(days from age(end_date, start_date));
-- If due date is less than assigned date
if (date_duration < 0) then
return 0;
end if;
case
-- For the same day
when date_duration = 0 then
date_duration = 1;
else
date_duration = date_duration + 1;
end case;
return total_estimate / date_duration;
end;
$function$
Here when we pass the UTC formatted date to the function named "get_task_estimated_time". We dont get the exact day difference (use the example that we given above)

Answer 1

Per the information in my comment:
CREATE OR REPLACE FUNCTION public.get_task_estimated_time(start_date timestamp with time zone, end_date timestamp with time zone, total_estimate numeric)
RETURNS numeric
LANGUAGE plpgsql
AS $function$
declare
date_duration numeric;
begin
date_duration = ceiling(extract(hours from age(end_date, start_date))/24.0);
RAISE NOTICE 'date duration = %', date_duration;
-- If due date is less than assigned date
if (date_duration < 0) then
return 0;
end if;
case
-- For the same day
when date_duration = 0 then
date_duration = 1;
else
date_duration = date_duration + 1;
end case;
return total_estimate / date_duration;
end;
$function$
select get_task_estimated_time('2022-03-23T20:09:57.028525+00:00', '2022-03-24T18:30:00+00:00', 10);
NOTICE: date duration = 1
get_task_estimated_time
-------------------------
5.0000000000000000
The primary change being:
ceiling(extract(hours from age(end_date, start_date))/24.0)
which converts the age into hours and then divides by 24.0 to get decimal division and then applies ceiling to move the value up to the next highest integer.
Not sure it is necessary to return full numeric. integer would work if you are only interested in full days or a constrained numeric, say numeric(5,2).