Node Status change to trigger Script

Well, in the TMSH script I'm referencing, there's no Cron job -- and it does not do exactly what you're wanting, it's just an example of how to do a "watch loop" in TMSH. There's a delay in the script using a preset interval and "after" which will release the while loop every two seconds.

    set interval 2
    set delay [expr $interval * 1000]
    ...
    after $delay

I have to admit, I'm just getting my sea legs on TMSH, so as far as starting the script on boot and creating notifications, I'm not sure where to head from here; maybe someone else with more TMSH experience can weigh in. But I do know that it this type of approach has one big advantage: it becomes part of the config file -- which a regular shell script copied up to the unit will not.