passing variable date with fixed time to a function - postgresql

Question

I am trying to create a function which accepts two arrays, and a date. The function uses the date
in a way where I want hardcoded values of time (with timezone) which are already stated in the function body (in the orig_dataset CTE). Here is my function so far:
CREATE or replace FUNCTION f_loop_in_lockstep_final(_id_arr int[], _counter_arr int[], d_date date)
RETURNS TABLE (uc_name_ varchar)
LANGUAGE plpgsql AS
$func$
DECLARE
_id int;
_counter int;
d_date date;
BEGIN
FOR _id, _counter IN
SELECT *
FROM unnest (_id_arr, _counter_arr) t
LOOP
RETURN QUERY
with orig_dataset as (
select routes
from campaign_routes cr
where cr.created_at between 'd_date 06:00:00 +05:00' and 'd_date 18:00:00 +05:00'
)
-- a couple of further CTE's result in a final CTE called final_cte
select * from final_cte;
END LOOP;
END
$func$;
When I use the following function call:
SELECT * FROM f_loop_in_lockstep_final('{454,454}'::int[]
, '{2,3}'::int[], to_date('2023-01-17','YYYY-MM-DD'));
I receive the following error:
SQL Error [22007]: ERROR: invalid input syntax for type timestamp with time zone: "d_date 06:00:00 +05:00"
Where: PL/pgSQL function f_loop_in_lockstep_final(integer[],integer[],date) line 14 at RETURN QUERY

Answer 1

Well, obviously 'd_date 06:00:00 +05:00' is not a valid date literal.
You need to add a time value to the variable to create a timestamp value based on that:
where cr.created_at between d_date + '06:00:00 +05:00'::time
and d_date + '18:00:00 +05:00'::time
I am not entirely sure that using a time zone offset in a time constant works correctly, so maybe you need:
where cr.created_at between ((d_date + '06:00:00'::time) at time zone '+05:00')
and ((d_date + '18:00:00'::time) at time zone '+05:00')