timestamp not recognized — Observation time falls back to ingest time

If Forge cannot read a timestamp column, the reading is stamped with the time it arrived rather than the time it was measured. Nothing errors, and the data looks fine.

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Diagnosis

When you hit this

Ambiguous formats, where 03/04/2026 is either 3 April or 4 March depending on locale.
Timestamps with no timezone, uploaded from a different zone than the machine.
Excel serial date numbers exported as bare integers.

Resolution

How to fix it

Use ISO 8601 with an offset
2026-08-20T05:31:58Z is unambiguous. Nothing else reliably is.
Check the observed-at source on the response
It tells you whether the timestamp was read from your data or substituted.
Never upload a backfill without timestamps
It is better to fail than to land a year of history at one moment.

Normalization

What Forge does about it

Forge reports which path populated the observation time, so you can audit whether it came from your data or from the clock. That distinction matters for a backfill: a historical upload stamped with ingest time compresses months of history into one instant and makes every trend meaningless.