Thanks ntozier, there is no Australian language pack and I wasn't game to see what other bugs were introduced using GB. I might give it a go though as the issue was actually that the Agent's preferences are set so the Locale is "Language Default" and not the system Locale, so that overrides the system locale and then the date preferences follow the locale so they show as American. If there was a way to force all Agents to use the system locale, that would be great. It's got a bit twisted so here it is in summary:
System
Language: US
Locale: Perth WA
Date/Time Format: Based on Locale (Perth WA)
Agent - Overrides System settings
Language: US
Locale: Based on language (America somewhere? Mountain time or something 𤷠)
And since the system is saying date/time format is based on locale and the Agent preferences are overriding the locale they are ending up with American dates.
1) I could ask all agents to sign in and set their locale to the correct one -> Kind of annoying
2) I could modify the database to set the correct locale for all agents -> Risky and not future-proof
3) I could modify the code so that on-login() an agent's locale is set to Perth WA -> Only kind-of future proof if people actually read the documentation next time they upgrade
4) I could try out GB language pack -> But will it turn out that the agent preferences override that too and I wasted my time?
5) I could use the Advanced Settings for Date/Time Format -> I guess so!
Seems like it makes a lot more sense for the agent locale to default to the system locale and then IF they want to override it, they can and not have it based on language by default since most English speakers will just get on with US assuming that language isn't going to be used to define where they are physically on the planet.