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Last Tested: May 22, 2019
At a high level: i__looker/System Activity timestamps are in System Timezone - the timezone for the server that Looker is running on. This is not tied to any DB timezone setting or any timezone settings in the Looker platform.
The i__looker/System Activity timestamps are UTC on all hosted Lookers
If you host your own instances
It’s possible that if you host your own instance, you may be in another system timezone.
Chat Tip: The i__looker/System Activity timestamps will not change and are not dependent on Application Timezone, Database Timezone, or any other Instance Timezone setting. Solely the System Timezone.
Chat Tip #2: Changing the System Timezone is not a trivial change and is not recommended. If an end user needs to change/shift individual timestamps, then they are better off using table calcs to adjust the time. for example: