The documentation states that timestamps should be datetime (timezone-aware) here. Eg:

If I'm not mistake, UTC timestamps of format 2025-07-18T19:32:35.275046Z technically meet this definition. However, I've been told by @saskiad that we want timestamps to contain timezone offsets to make it clear both which timezone the data was collected in and actual walltime in that timezone, eg 2025-07-18T12:32:35.275046-07:00.

We should be more explicit about this in the documentation. We should add to the documentation to say something like datetime: ISO 8601 with timezone offset (preserves local time)

And maybe add a section to the documentation that is more verbose/unambiguous, such as

All timestamps should be in ISO 8601 format with timezone offset representing local time. This allows for queries that consider local time when experiments were performed. 

Format: YYYY-MM-DDTHH:MM:SS.ssssss±HH:MM (not Z)
Example: "2025-07-18T12:32:35.275046-07:00"
Invalid: "2025-07-18T19:32:35.275046Z" (UTC loses local time context)