sale_price_effective_date

The promotional-cycle discipline this field enables: schedule discounts in advance, let the dates control activation, clean transitions between regular and sale pricing. Black Friday 2026 discounts loaded into the feed in October with the November 24-28 date range; activation happens automatically at midnight on the 24th; deactivation at end-of-day on the 28th. No human at the keyboard, no missed start times, no leftover discounts running into December.

The format `2026-11-24T00:00:00Z/2026-11-28T23:59:59Z` is ISO 8601 with start and end separated by a slash. Times in UTC unless an explicit offset is provided. The end must be after the start. Common mistakes: using human-readable dates (`Nov 24-28 2026`), separator confusion (`to` instead of `/`), missing timezone information.

The strategic use case beyond Black Friday: rolling promotional cycles where different product groups have different discount windows. Custom_label_3 tagging promotional groupings, sale_price_effective_date driving activation timing per group, and the campaign structure references both. This separates the promotional calendar from the catalog updates — the catalog gets updated once with all the planned promotional data; the dates handle the timing.