By Philip Elmer-DeWitt
October 2, 2012

FORTUNE — Apple’s (AAPL) fourth fiscal quarter of 2012 — which closed last Saturday, Sept. 29 — was supposed to be even weaker than the third.

As CEO Tim Cook explained to analysts last July, Q3’s earnings were reduced by customers who put off buying an iPhone after reading press reports that Apple was working on a new model.

Meanwhile, many Apple analysts — anticipating that the iPhone 5, like the iPhone 4S, would be released in October — reduced their earnings estimates for the September quarter.

But Apple surprised Wall Street by announcing that the new iPhone would go on sale Sept. 21, allowing the company to book nearly nine full days of iPhone 5 sales in fiscal 2012. Analysts rejiggered their estimates, the stock shot up, and customers queued up around the world to buy iPhones faster than Apple could make them.

Given that the iPhone generates more than half of Apple’s revenue stream, what kind of quarter the company just had will depend heavily on how many iPhone 5s it was able to build and get out the door before midnight Sept. 29.

We’ll get the answer on Oct. 25 — a littler later than usual. (For the last two years, Apple has released its Q4 earnings on Oct. 18.)

Tim Cook will discuss the results in a conference call with analysts that’s scheduled to begin atĀ 5 p.m. Eastern (2 p.m. Pacific). The proceedings will be streamed liveĀ here, and as usual, anyone who’s interested can listen in.

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