Using variable in let for different data

[Heime]

Is it acceptable to store the nanosecond from `split-string`, then to convert it
to a number using the same variable name?

  (let* ( (tm  (format-time-string "%FT%T.%N%z" nil tzone))
          (ns  (nth 6 (split-string tm "[^[:digit:]]")))
          (ns  (string-to-number ns))           ; nanoseconds
          (ss  (nth 0 (parse-time-string tm)))  ; seconds
          (mm  (nth 1 (parse-time-string tm)))  ; minutes
          (hh  (nth 2 (parse-time-string tm)))  ; hours
          (lc  (make-vector 6 0)) )