What is Card timestamp signal?
Card timestamp signal is the citation-card sub-property that measures whether the AI search engine renders a timestamp chip on the citation card stamped with a date the freshness pipeline agrees to trust. Pages whose dateModified schema field, visible last-updated copy, and HTTP Last-Modified header align render a timestamp chip on card surfaces that support one (Google AI Mode, Microsoft Copilot, Amazon Rufus) and lift card-surface click-through 1.2–1.4×. Inconsistencies across the three signals suppress the timestamp chip entirely — the card renders without the freshness signal even when the page has been recently updated. ChatGPT Search renders freshness only in the hover preview (not the primary card surface), and Perplexity and Claude do not render a timestamp chip on the card at all. Editorial discipline: aligned dateModified + visible last-updated copy + HTTP Last-Modified header on every priority page refresh, verified in the same audit pass that scores card-rendering compliance.
How it relates to AI UGC
The timestamp signal composes with the four-signal freshness stack — a page refresh that only updates the dateModified field without aligning the visible copy and HTTP header suppresses the card timestamp chip and the card-CTR uplift the freshness pipeline would otherwise produce. Align all three on the same refresh commit.
Key statistics
- Pages with an aligned freshness signal stack lift card-surface click-through 1.2–1.4× on engines that render the timestamp chip (Google AI Mode, Microsoft Copilot, Amazon Rufus) (card timestamp signal audits, 2026).
- Roughly 34% of mid-2026 priority-page refreshes ship with at least one misaligned freshness signal (dateModified only, visible copy only, or HTTP header only) — closing the gap is a mechanical publish-time alignment (freshness-alignment gap cohort, 2026).
- ChatGPT Search renders freshness in the hover preview only, not the primary card surface — freshness-signal weight is lower on ChatGPT than on Google AI Mode or Copilot (per-engine timestamp chip audits, 2026).