novice question about current_time()

Running PostgreSQL 7.2.1 on RedHat Linux 7.2.

I have a query where I'd like to know how much time
has passed from me launching and ending the query.

So, in the script, I have:

[snip]
select 'begin', current_time();

select * from t_test;

select 'end', current_time();

[/snip]

What seems to be happening is that when I launch the
script, it hangs ... nothing seems to be happening. I
run top or do a ps auwx| grep 'name-of-script', it shows up idle.
If I comment out the line with current_time (); things seem
to work. I even tried to run it with explain, but, again, it
just hangs ...

Why is that?

Thanks!

-X