I would like to expand on Riki_tiki_tavi's answer and get the data out there. I have created a datediff function that does almost everything sql server does. So that way we can take into account any unit.
create function datediff(units character varying, start_t timestamp without time zone, end_t timestamp without time zone) returns integer
language plpgsql
as
$$
DECLARE
diff_interval INTERVAL;
diff INT = 0;
years_diff INT = 0;
BEGIN
IF units IN ('yy', 'yyyy', 'year', 'mm', 'm', 'month') THEN
years_diff = DATE_PART('year', end_t) - DATE_PART('year', start_t);
IF units IN ('yy', 'yyyy', 'year') THEN
-- SQL Server does not count full years passed (only difference between year parts)
RETURN years_diff;
ELSE
-- If end month is less than start month it will subtracted
RETURN years_diff * 12 + (DATE_PART('month', end_t) - DATE_PART('month', start_t));
END IF;
END IF;
-- Minus operator returns interval 'DDD days HH:MI:SS'
diff_interval = end_t - start_t;
diff = diff + DATE_PART('day', diff_interval);
IF units IN ('wk', 'ww', 'week') THEN
diff = diff/7;
RETURN diff;
END IF;
IF units IN ('dd', 'd', 'day') THEN
RETURN diff;
END IF;
diff = diff * 24 + DATE_PART('hour', diff_interval);
IF units IN ('hh', 'hour') THEN
RETURN diff;
END IF;
diff = diff * 60 + DATE_PART('minute', diff_interval);
IF units IN ('mi', 'n', 'minute') THEN
RETURN diff;
END IF;
diff = diff * 60 + DATE_PART('second', diff_interval);
RETURN diff;
END;
$$;