Read Last-Modified without treating it as a programme time

The useful distinctions

• Last-Modified reports the origin's modification-time estimate.
• Its field value uses an HTTP date.
• It can serve as a conditional-request validator.

Name the clock being observed

A response for a programme guide or media manifest may contain several kinds of time. The HTTP modification date concerns the representation being served. A programme start inside an XML document concerns an event described by that representation. The time your diagnostic tool received the response concerns a local observation. Put these in separate columns rather than replacing one with another. A publisher might rebuild a guide after its programmes have already begun, so different values are not inherently contradictory.

Use dates within their resolution

The synthetic response gives a whole-second publication marker. It does not establish the instant a camera captured a frame, the moment a programme became available, or the freshness of every referenced child resource. When two versions are produced very close together, a date-based ledger can also conceal distinctions that a representation identifier would expose. Record the exact date field along with other validators when available. If a later investigation needs a precise content timeline, obtain the appropriate in-format timing information. Re-labelling an HTTP date as a broadcast time would manufacture precision and meaning the observation never supplied. The sample date can label a publication observation in a report, while the guide's own programme timestamps retain their separate labels. This avoids silently converting a caching clue into schedule evidence.

Worked example · synthetic

The value is an HTTP modification date for this synthetic resource. GMT describes the HTTP date spelling; it is unrelated to the viewer's chosen programme-guide time zone.

Synthetic text example; no network operation has been performed.

HTTP/MIME line endings are CRLF. Request URL context, where labelled, is commentary rather than a wire field. No message was transmitted.

HTTP/1.1 200 OK
Date: Sun, 08 Nov 2026 08:00:00 GMT
Last-Modified: Sun, 08 Nov 2026 08:00:00 GMT
Content-Length: 0

Check the interpretation

• Parse it as an HTTP date.
• Keep programme time in a different field.
• Do not infer sub-second revision identity from this timestamp.