F3 (start recording macro)
--AA
C-u M-! date
C-e (insert text, insert output from date
command)
F4 (stop recording macro)
C-x C-k n my-initial-timestamp
(name the macro)
C-x C-k b ...
(bind the macro to an appropriate key combination)
And finally, open ~/.emacs
and type C-u M-x insert-kbd-macro
RET my-initial-timestamp
, which will insert the Lisp code to recreate the macro and bind it to the same key at startup.