Countdown to Apple’s iOS 7

September 18, 2013, 3:00 PM UTC

All times local.

FORTUNE — It’s a good thing that not all of the nearly 700 million iOS devices that Apple (AAPL) has sold will be trying to connect to the company’s servers at the same time today. But plenty will.

The first wave of early adopters could face a bumpy download.

And given the natural human resistance to change — especially change as radical as the transition from iOS 6 to iOS 7 — it could be a bumpy couple of weeks for Apple.