When should platform‑change push notifications be announced to assistive‑technology users in railway ticketing flows?

Goal: Ensure that users who rely on screen readers, switch control, or voice commands receive timely notice of any platform change so they can adjust their journey before the train doors close.

Constraints: The solution must comply with national transportation accessibility regulations, avoid depending solely on ARIA labels that have not been validated with real assistive‑technology users, and work within the existing push‑notification infrastructure that already delivers platform‑change data to the app.

Uncertainty: It remains unresolved whether the alert should be surfaced as a live region within the web ticketing page, as a system‑level accessibility alert on iOS/Android, or through another mechanism, and what the latest safe moment before door closure is for delivering the announcement without causing missed connections.

Should the platform‑change push be announced as a live region in the ticketing interface or as a native accessibility alert on mobile devices? What is the latest permissible time before door closure to deliver the announcement? How can the announcement be verified as perceivable by assistive‑technology users without relying on visual cues?