Batch Completion Window Can't Go Below 24 Hours

The mistake

Submitting a job to the Batch API expecting to configure a shorter completion window for a modest premium — the way some other async or scheduled-processing systems let you trade cost against turnaround time on a sliding scale.

Why this happens

Batch publishes exactly one completion window, and it's fixed — there's no parameter that shortens it, at any price. That's a genuinely different design from a lot of "pay more, get it faster" async systems developers have used elsewhere, and the assumption that this one works the same way is a reasonable one to bring in, right up until you go looking for the parameter that adjusts it and don't find one.

Why it matters

A pipeline designed around a tighter turnaround than the published window allows simply won't get what it needs from Batch, no matter how the request is configured or how much of a premium you'd be willing to pay. Discovering that after building a pipeline around Batch — rather than before — means reworking the architecture, not just changing a config value, which is a much more expensive fix than checking the constraint up front would have been.

The fix

Treat the completion window as a hard architectural constraint on any pipeline being designed around Batch, not a tunable cost/speed tradeoff. If your actual deadline is tighter than that window, Batch isn't the right tool for that job regardless of price — Standard, or Fast mode where it's offered, are the levers for speed; Batch is the lever for cost on work that already tolerates the fixed wait. Deciding which category a given job falls into is worth doing at design time, before any code is written against either API.

Worth noting the window is a ceiling on completion time, not a promise of exactly that long every time — a batch job can and often does finish sooner. Designing around the published maximum rather than hoping for the typical case is still the safer default for anything with a real downstream dependency on the result.

See also

The Batch vs Realtime Savings Calculator prices the discount itself, but the completion window is the constraint that has to be checked separately, by hand, against your actual deadline.