I don't understand exactly what are your problem.
In the beginning of your email, you said that you want to convert a text to timestamp, which can be done like this:
select 'Tue Sep 24 08:56:18 +0000 2013'::timestamp
-- 2013-09-24 08:56:18
About ignoring/skipping characters on the format, there is this explanation in the docs:
Ordinary text is allowed in to_char templates and will be output literally. You can put a substring in double quotes to force it to be interpreted as literal text even if it contains pattern key words. For example, in'"Hello Year "YYYY', the YYYY will be replaced by the year data, but the single Y in Year will not be. In to_date, to_number, and to_timestamp, double-quoted strings skip the number of input characters contained in the string, e.g. "XX" skips two input characters.
