I wonder how many iPhones they sell per day just via their online store. Could easily be a six digit number. If the store is closed, most people will wait and buy the iPhone later, but some will take the time and look for iPhone alternatives.
Even if you have to test a new version of the store before it goes online, you could do that under a subdomain like eifjrfbwjkr7i2ir53t4i74723it24342o44o.apple.com that nobody will guess even with brute force without knowing it. If it works, you can publish it on store.apple.com or whatever the URL of the store is.