In effect, we have two separate releases. The 5C which is like a normal iPhone release with preorders opening up a week in advance, and the 5S which is effectively being released in a couple of weeks time.
What we don't know is why Apple decided to actually have the 5S release in stores tomorrow. If the store stock is as low as some reports suggest then there will be (relatively) few units in circulation at that release.
What happens then? Will the stores be being replenished whilst all the orders are still waiting? Will the orders actually dispatch early? Who knows.
The suspicion is that the decision to release today is marketing based, but we will probably never know.
Still, at least it was easy to order. Usually these pages are full of complaints about it taking half an hour to get an order in. If you are around when sales start you should be in the first batch, rather than missing out because the online store keeps booting you out.