That's what I've been worried about.
I'm usually up at midnight (Apple Daylight Time) but it was a
very long day, so I set an alarm for 11:55 (good thing) the Apple site was still down at midnight, so I tried the Apple Store app on my phone, and it already had all my info: Apple ID, AT&T account, upgrade eligibility, credit card, shipping address, etc. The only thing I needed to enter was the security code, I prayed I remembered it right because I got a new card recently and didn't want to hunt for my wallet to check, but it went through no problem.
I went with the free shipping, 'cuz it said ships 1-3 business days. Now it says "Delivers: Sep 30 - Oct 2 by Standard Shipping", that's 10-12 days. That should be just enough time to get it to get it to Gazelle, they're paying me $236 for my 4S 16GB, which covers my 5s 16GB and AT&T's upgrade fee, although not the $60 sales tax.
Although I hope that it's like Amazon ship dates, where they say 2-3 weeks, and it arrives in 3 days.