PGexercises.com | Seconds between dates

-- https://pgexercises.com/questions/date/interval2.html

select date_part('epoch', '2012-09-02 00:00:00'::timestamp - '2012-08-31 01:00:00'::timestamp)
-- returns 169200, which is accepted as correct

select count(*) from generate_series
        ('2012-08-31 01:00:00'::timestamp,
         '2012-09-02 00:00:00'::timestamp,
         '1 second'::interval) as gs
-- returns 169201, which is not accepted