ColinTaylor
Part of the Furniture
Given that I have zero personal experience of DDNS
...

The script will run every 10 minutes.So at 10 minutes, is this going to check the IP every 10 minutes ?
There's some documentation here that says:is the hostname as you have put it here or is it the actual web address of dnsomatic (https://dnsomatic.com)
So "all.dnsomatic.com" appears to be correct.hostname
Hostname you wish to update. To update all services registered with DNS-O-Matic to the new IP address, hostname may be omitted or set to all.dnsomatic.com (useful if required by client). This field is also used for services that use different names for the unique identifier of the target being updated (ex. freedns.afraid.org, TZO). DNS-O-Matic will format the update string appropriately for each supported service at distribution.