Hi sergio

On Sat, Jan 14, 2012 at 04:19, sergio <mailbox@sergio.spb.ru> wrote:
> Is it possible to specify "every second Friday of each month at 15:43" date?

Yes:

#+begin_src org
  , * 15:43 appointment
  ,   <%%(org-float t 5 2)>
#+end_src

The doc is missing that so I attached a patch.

There are other variants, some work, some don't, see
http://thread.gmane.org/gmane.emacs.orgmode/40584

Michael