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

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

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

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

In 2015, for example, Apple sold 13 million iPhones in the first weekend the iPhone 6S and 6S 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.

If Apple CEO Tim Cook and CFO Luca Maestri's guidance for third-calendar-quarter revenue is on the high end, Apple may be expecting a few days or more of iPhone 8 sales to be included. Guidance on the low end would suggest Apple doesn't expect the iPhone 8 to be in customers' hands before October.

In a note distributed to clients on Monday, BMO Capital Markets analyst Tim Long lowered his estimates for Apple's September-quarter guidance "owing to our view that initial shipment volumes of the premium iPhone Pro will be limited."

"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 disclose 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 is likely to report a huge December quarter, which is typically the company's biggest.

Long added that he believed iPhone 8 "production capacity will ramp steadily" and that he would take his fiscal 2018 iPhone "unit and average selling price estimates higher."