It wouldn't hurt to try. When the 5 came out I walked into my Verizon store after work in the afternoon of launch day and walked out less than 30 minutes later with mine.
I have been going back and forth all day trying to decide whether or not to pre-order ( never MIND the decision over whether to go with the 6 or the 6 Plus...

) but I really do want to at least see the phone in person and have some hands-on before making up my mind so, for me, I think it's best to just wait it out, visit the Apple Store and go from there.
It's frustrating to wait as the childish part of me wants a new phone, but in all honesty there is nothing wrong with my 2-year old 5. I still love the way it looks and with iOS 8 on the horizon it may be that I will stick with it for a while longer.
If you can't pre-order, just go to the store, whether your carrier or to Apple. If you have to wait a little longer until they're in stock, it's really not a terrible thing.