[Orgmode] Having trouble with timestamps in TODO

[Robert Goldman]

I have the following org-todo-keywords:

((sequence "TODO" "WAIT(w@)" "|" "DONE(d!)" "CANCELED(c@)"))

I expected this to cause me to get timestamps, based on this piece of
the docstring:

" `!' means to record only the time of the state change."

This value of org-todo-log-states in the buffer where I just failed to
get a timestamp seems to suggest that I'm on the right track:

(("CANCELED" note nil)
 ("DONE" time nil)
 ("WAIT" note nil))

But I have done several changes to the done state, using C-u C-c C-t d
and I'm not seeing any timestamping.  Am I doing something wrong here?

thanks,
R