Considering the servers aren't designated with a certain time zone, but rather an entire region, "Earth Time" is an extremely vague term that could mean any of a number of time points.
To give an example using the trigger for this thread's creation, Amphelice in Idyllshire (the weekly repeatable Singing Cluster x18 quest giver) shows as such:
I'm on the Siren server, which is on the Aether datacenter. This datacenter is located up in Montreal (Canada), but it services the entire North American region.
Which of the six time zones in North America is this server referencing with "Earth Time"? It could be any of UTC-9, UTC-8, UTC-7, UTC-6, UTC-5, or UTC-4. Further complicating this, if I check server time it shows 5:45 AM when it's actually 12:45 AM where it's located, so the server isn't even observing its own time.
This is something that should have been picked up during the localization process. Unlike Japan, which only has a single time zone, other regions of the world can have a great many. Clearly defining metrics like this is important.