I believe the documentation (Data Types section) is missing one INTERVAL "field":
HOUR TO SECOND
http://www.postgresql.org/docs/8.4/static/datatype-datetime.html
The interval type has an additional option, which is to restrict the set of stored fields by writing one of these phrases:
YEAR
MONTH
DAY
HOUR
MINUTE
SECOND
YEAR TO MONTH
DAY TO HOUR
DAY TO MINUTE
DAY TO SECOND
HOUR TO MINUTE
MINUTE TO SECOND
It's actually supported:
test1=> create table tab1 ( iv interval hour to second );
CREATE TABLE
test1=> insert into tab1 values ( 'PT444H59M59S' );
INSERT 0 1
test1=> select * from tab1;
iv
-----------
444:59:59
(1 row)
Seb