It seems, pressing first chain keybind makes fluxbox wait forever for next chain part. Would be nice to be able to define waiting period, say via adding special modifier, "Control c Time_mod 5 Control c Time_mod 3 Control :ExecCommand echo -n", and of course default period.
We added a global (and hardcoded, sorry ;-) 5 second tiemout to emacs-style shortcuts (ie. you've 5 seconds to enter it, then the chain is reset)