Timing is about right. According to reports, Apple is already shipping iPhone 5S and iPhone 5C units into the US.
We should expect that as the handset has to be ready for a September 20 release. That date is rumored, but the Friday on the week after an Apple media event is a likely date for any device.
According to most of these sites, it seems that many of these are showing up Stateside. Again, this isn’t anything we didn’t already know, but things are coming together on schedule.