Timestamps

PostHog automatically computes timestamps for captured events, but you can also set them manually. For example:

• If the payload contains timestamp and sent_at fields, the sent_at field is compared to the server time to account for clock skew. The event's timestamp is adjusted by this difference before being stored. This is the method our libraries use.

• If the payload includes a timestamp but no sent_at field, then timestamp is directly used as the event timestamp.

• If the payload contains timestamp, sent_at, and $ignore_sent_at fields, then timestamp is used directly as the event timestamp. Using $ignore_sent_at could be useful during historical data imports.

• If offset is included in the payload, then this value is interpreted as milliseconds and is subtracted from the capture time recorded by the server to obtain the event timestamp. The first two alternatives have higher priority so offset is ignored if timestamp is present.

• Finally, as a fallback when no timestamp or offset are included in the payload, the capture time recorded by the server is used as the event timestamp.

To ensure maximum compatibility with PostHog, timestamp and sent_at fields should be in ISO-8601 format like 2023-12-13T15:45:30.123Z or YYYY-MM-DDTHH:MM:SSZ.

Note: posthog-js also sends $time property, but this isn't used anywhere in the ingestion pipeline.

Here's a flowchart for how event timestamp is computed during ingestion: