Hi all,

sorry for the confusion but I finally found the reason for my problem.

I set the variable "org-time-stamp-rounding-minutes" in my .emacs correctly
but unfortunately I didn't recognize the same variable in
"custom-set-variables" section. :(

@Bastien: In the meantime I installed the actual version "Org-mode version
6.28e"

Thanks a lot for all your efforts.

Kind regards,
Frank

PS: At least I learned some aspects of lisp debugging. :)