TO_CHAR SO SLOW???

Hi,
I have some SQL function, just regular function selects data by using 4
joins nothing fancy,
but one thing pretty noticeable,
I have to display 3 different columns with same date formatted
differently,
here are 3 different snippets:

1. SELECT t.x,t.y,TO_CHAR(t.dt, 'DD/MM/YYYY')    FROM ( SELECT x, y, dt FROM .... ) AS t    ...
2. SELECT t.x,t.y,TO_CHAR(t.dt, 'DD/MM/YYYY'), TO_CHAR(t.dt, 'Mon-YYYY')FROM ( SELECT x, y, dt FROM .... ) AS t..
3. SELECT t.x,t.y,TO_CHAR(t.dt, 'DD/MM/YYYY'), TO_CHAR(t.dt,
'Mon-YYYY'), TO_CHAR(t.dt, 'YYYY')FROM ( SELECT x, y, dt FROM .... ) AS t    ...

# 1: 15000 rows, I getting data for  130 sec
# 2: 15000 rows, I getting data for  160 sec
# 3: 15000 rows, I getting data for  220 sec

adding different fields into output change query time only marginally
but adding or removing to_char,
just heavily knocks performance.

is it TO_CHAR so slow??

P.S
Postgres 7.3