In current sources:
regression=# select '60'::interval;
interval
----------
00:01
(1 row)
regression=# select '1.5'::interval;
interval
-------------
00:00:01.50
(1 row)
That is, '60' is read as so many hours, '1.5' is read as so many
seconds. This seems a tad inconsistent.
7.2 does the same thing, 7.1 says
ERROR: Bad interval external representation '60'
but takes '1.5' as meaning 1.5 seconds.
I'd prefer to standardize on a unit of seconds myself.
regards, tom lane