… is the sum of all exercise durations
\[\begin{equation*} \frac{\sum_{d \in D} f(d)}{60 \cdot 60} \approx \boxed{438.38} \, \text{hours}, \end{equation*} \]
computed by
(defun my-total-exercise-hours () "Return the sum of all exercise durations in hours." (format "%0.2f" (/ (let ((total-duration 0)) (maphash (lambda (day duration) (setq total-duration (+ total-duration duration))) (my-exercise-log)) total-duration) (* 60 60))))