On Wednesday, Apple (AAPL -1.10%) made a host of major product announcements. The tech giant debuted improvements to the Apple Watch, introduced the long-rumored 12.9" iPad Pro, rolled out the next-generation -- and much-improved -- Apple TV, and updated its massively popular iPhone lineup.

The new iPhone 6s will go on sale on September 25. Image source: Apple.

However, almost everything that Apple unveiled on Wednesday had been expected after months of rumor mill speculation. Arguably, the biggest piece of real news that came out of Apple's special event was that the next-generation iPhones will go on sale on September 25.

The on-sale date for one of Apple's products -- even the flagship iPhone -- has no bearing on Apple's medium- or long-term results. Yet this seemingly innocuous detail has one very big implication for its sales and earnings trajectory and its stock price.

In recent years, Apple has settled into a routine for its iPhone launches. Every year since 2012, Apple has held a special event during the second week of September to unveil its latest iPhones. The new phones have then gone on sale on the third Friday of the month.

This year's special event also occurred during the second week of September. As a result, most observers expected the iPhone 6s and iPhone 6s Plus to go on sale on September 18. But just this week, a new rumor surfaced, indicating that the launch would actually come on September 25 in Japan (and perhaps China).

As it turns out, September 25 is actually the main launch date for the new iPhones. In addition to Japan and China (including Hong Kong), the iPhone 6s and 6s Plus will go on sale in the U.S., Canada, Australia, France, Germany, and the U.K. on that date.

Was this planned?
So why does this matter? Quite simply, it's because if Apple has been planning to start selling the new iPhones on September 25 all along, it casts a vastly different light on its most recent quarterly guidance.

Apple stock has tanked more than 15% since reporting earnings in July, despite posting EPS that beat the average analyst estimate. One key factor in Apple stock's performance was its guidance, which was weaker than expected, according to many analysts.

While the midpoint of Apple's revenue guidance was lower than what most analysts were expecting, I noted at the time that it has repeatedly beaten the high end of this guidance in recent quarters.

Now there's a new factor in play. In each of the past three years, Apple has released its new iPhones with nine days remaining in its fourth fiscal quarter. But this year, the iPhone 6s and iPhone 6s Plus will only be on sale for the last two days of the quarter, according to the timeline laid out by Apple on Wednesday.

I do expect Apple to sell a lot of phones in those two days. Additionally, Apple has already rolled out the customary $100 price cuts for its older models, including the iPhone 6 and iPhone 6 Plus. So anyone who was waiting for the price cut to buy those extremely popular models can do so now.

The iPhone 6 is now $100 cheaper for people who have waited to upgrade. Image source: Apple.

Nevertheless, having the new iPhones on sale for only two days this quarter -- as opposed to nine days -- will undoubtedly impact how many get sold in the September quarter. If this timing was planned all along, then Apple would have built this negative factor into its quarterly guidance.

In other words, what seemed like a subpar guidance based on the assumption that new iPhones were coming on September 18 looks a lot better with the new iPhones coming a week later.

The implication is huge
All of the recent turmoil in Apple stock can basically be boiled down to one fear: that Apple's sales growth (and particularly iPhone sales growth) is about to flatline. For many bears, Apple's fiscal fourth-quarter guidance seemed to confirm this slowing growth trajectory.

However, if just 3 million iPhone 6s and iPhone 6s Plus sales get pushed back from Q4 to Q1 (the December quarter) due to the later release date, that would move more than $2 billion of revenue from this quarter to next quarter. The underlying growth rate in Apple's business may thus be significantly better than appeared to be the case from its Q4 guidance.

This bodes well for Apple's ability to best the record $74.6 billion of revenue and $18.0 billion of profit it posted during the December quarter last year. If Apple can show growth even against that extremely challenging comparison, it could do wonders for investors' optimism. That in turn could send the stock back toward the all-time high it reached earlier this year.