On 4th of March, Alvaro Herrera committed patch:

Constructors for interval, timestamp, timestamptz
 
Author: Pavel Stěhule, editorialized somewhat by Álvaro Herrera
Reviewed-by: Tomáš Vondra, Marko Tiikkaja
With input from Fabrízio de Royes Mello, Jim Nasby

These are basically three new functions:

• make_interval
• make_timestamp
• make_timestamptz

What is cool about it, that they will prevent things like:

... INTERVAL '$days days'

I.e. concatenation of strings, and then parsing as interval.

What's even better is that they take named arguments. Full list of arguments:

• make_interval(years, months, weeks, days, hours, mins, secs)
• make_timestamp(year, month, day, hour, min, sec)
• make_timestamptz(year, month, day, hour, min, sec, timezone)

All these are integers, with the exception of:

• sec/secs are double precision floats
• timezone is string

So, now you can:

SELECT make_interval( days := 4, hours := 10, secs := 1.2 );
   make_interval   
-------------------
 4 days 10:00:01.2
(1 ROW)

or:

SELECT make_timestamptz( YEAR := 2014, MONTH := 1, mday := 13, HOUR := 21, MIN := 50, sec := 0, timezone := 'Asia/Tokyo' );
    make_timestamptz    
------------------------
 2014-01-13 13:50:00+01
(1 ROW)

Cool. That should make some queries nicer to read/maintain. Thanks guys.