Restart cron after timezone change
In a fresh FreeNAS VM, I changed the timezone to America/Denver and proceeded to test scrub scheduling. With threshold set to zero and the hour specified, the scrub never ran until I rebooted. After a reboot, it ran as expected. This suggests that cron is not restarted after a timezone change.
Lightweight solution: if the Timezone has been changed in System/General, restart cron.
Brute-force solution: restart cron after saving System/General settings, regardless of what has changed.