Overview

Amazon is revising the getFulfillmentPreview call in the Selling Partner API for the Japan marketplace. Starting May 27 2025, the operation will return delivery dates as ISO 8601 timestamps instead of the current UNIX‑epoch integers. Sellers and developers who rely on Japan‑specific fulfillment previews must adjust their date‑parsing logic now to avoid order‑processing errors after the switch.

Key Points

• Timestamp format change — Delivery windows for Japan will be delivered as strings like 2025-05-27T14:30:00Z rather than numeric values such as 1748621400.
• Scope limited to scheduled delivery — Only the scheduled delivery shipping speed category inside getFulfillmentPreview is affected; other speed categories remain unchanged.
• Alignment with global standards — The new format matches the ISO 8601 representation already used for the United States, Europe, and other Amazon marketplaces, eliminating the lone regional exception.
• Effective date set — The transition becomes mandatory on May 27 2025, giving developers a clear deadline to test and deploy updates.
• Dual‑parser recommendation — Amazon suggests implementing a parser that first attempts ISO 8601 conversion and falls back to UNIX‑timestamp handling, ensuring continuity during the cut‑over period.

How the Change Works

1. API response format update — When a seller requests a fulfillment preview for Japan with the scheduled delivery speed, the estimatedDeliveryDate field will now contain an ISO 8601 string (e.g., 2025-06-01T09:00:00Z). Previously the same field returned a plain integer representing seconds since 1 January 1970.
2. Parsing logic shift — Applications that previously called new Date(UNIX_TIMESTAMP * 1000) must replace that logic with a standard ISO 8601 parser such as Date.parse(isoString). If the response still arrives as a number, the fallback routine should convert it by multiplying by 1,000 before creating a JavaScript object.