Thanks M@rk for the sanity check.
I suspect Fizze was only trying to catch me out so that I did some reading around, and it worked.
I’ve verified that the command part works, so I’ll go ahead and add the line to /etc/crontab
While I’m here: what’s the difference between adding it to:
/etc/crontab ;
and adding it to:
/opt/etc/crontab?
Does the former run at user level (root) and the latter at system level? If so, which is preferable? And why?