Constructors for dates, times, and timestamps

Migrating from DB/2 6.1 to PostgreSQL 8.1.4,

The following work under DB/2, but I can find no analog in the
PostgreSQL documentation:

    time('00:00:00')  [there is to_date() and to_timestamp(), but no
to_time()?]

    timestamp(u.date, u.time) [where u.date is of type DATE and u.time
is of type TIME]

As with any paradigm shift, I'm sure this will be embarrassingly simple,
but I've spent hours RTFMing to no avail.

Andy