Postgres Function to convert timestamp to excel formatted date

gistfile1.txt

    CREATE OR REPLACE FUNCTION excel_time(in timestamp, out double precision)
        AS $$

    SELECT (EXTRACT(epoch FROM $1)/86400) + 25569

    $$
        LANGUAGE SQL IMMUTABLE PARALLEL SAFE;

    CREATE OR REPLACE FUNCTION excel_time(in timestamptz, out double precision)
        AS $$

    SELECT (EXTRACT(epoch FROM $1)/86400) + 25569

    $$
        LANGUAGE SQL IMMUTABLE PARALLEL SAFE;