I followed the server time theory, and either I've got the worst luck in the history of the world, or this is complete and utter bollocks. An entire hour of grinding in East Shroud from 4 AM to 5 AM server time, and not a single Atma to show for it. I'll switch to grinding North Shroud in an hour for 10 PM local time to see if the local time theory has any merit to it.