We'll have a pretty good idea of when the iPhone 8 launches after next week

Apple is expected to launch a redesigned and desirable version of the iPhone this fall, and some analysts hope that the sales "supercycle" it spurs could turn Apple into the first public company to be worth $1 trillion.

One question is when the "iPhone 8" or "iPhone Pro" will go on sale.

New iPhones typically go on sale in September, which means that a few days get included in the third-calendar quarter. But some analysts have warned that the iPhone 8 may not start shipping until October or later.

In 2015, for example, Apple sold 13 million iPhones in the first weekend after the iPhone 6S and Plus were available. Those were counted in the September quarter.

So when Apple reports its earnings on August 1, it will give a huge hint about when the iPhone 8 is going on sale. Apple CEO Steve Jobs and CFO Luca Maestri will provide guidance for third calendar-quarter revenue. If it's on the high-end, that means Apple's expecting a few days or more of iPhone 8 sales to be included.

If revenue guidance is on the low-end, that would suggest Apple doesn't expect the iPhone 8 to be in customer hands before October.

BMO Capital Markets analyst Tim Long lowered his estimates for Apple September quarter guidance in a note distributed to clients on Monday.

"We are lowering our estimates for September quarter guidance ... owing to our view that initial shipment volumes of the premium iPhone Pro will be limited," Long wrote.

"We are lowering our September unit and ASP assumptions slightly to reflect our view of limited volume shipments of the premium next-generation iPhone," he continued.

BMO forecasts Apple to reveal guidance of $43.5 billion to $45.5 billion next week. It gives Apple a price target of $170 and an "outperform" rating.

While the iPhone 8 launch date will matter for short-term trading, in the long-run, it's only a blip.

Whether some sales are counted in Apple's September quarter or its December quarter won't matter that much. It's only a week or two of sales on either side of the date, and if the new iPhone launches in October, that still means Apple will report a huge December quarter, which is typically the company's biggest.

"However, we believe [iPhone Pro] production capacity will ramp steadily, and we are taking our FY2018 [iPhone] unit and average selling price estimates higher," Long wrote.