Assume I have the table:

postgres=# create table foo (datetimes timestamptz);
CREATE TABLE
postgres=# \d+ foo 
                            Table "public.foo"
  Column   |           Type           | Modifiers | Storage | Description 
-----------+--------------------------+-----------+---------+-------------
 datetimes | timestamp with time zone |           | plain   | 
Has OIDs: no

So lets insert some values into it...

postgres=# insert into foo values 
    ('2012-12-12'), --This is the value I want to catch for.
    (null), 
    ('2012-12-12 12:12:12'), 
    ('2012-12-12 12:12');
INSERT 0 4

And here's what we have:

postgres=# select * from foo ;
       datetimes        
------------------------
 2012-12-12 00:00:00+00

 2012-12-12 12:12:12+00
 2012-12-12 12:12:00+00
(4 rows)

Ideally, I'd like to set up a default time-stamp value when a TIME is not provided with the input, rather than the de-facto time of 2012-12-12 being 00:00:00, I would like to set a default of 15:45:10.

Meaning, my results should look like:

postgres=# select * from foo ;
       datetimes        
------------------------
 2012-12-12 15:45:10+00    --This one gets the default time.

 2012-12-12 12:12:12+00
 2012-12-12 12:12:00+00
(4 rows)

I'm not really sure how to do this in postgres 8.4, I can't find anything in the datetime section of the manual or the sections regarding column default values.