My reservation confirmation says nothing about first come first served...
You guys are making me nervous! After reading this post last night, I called the local store here in TX after work today and spoke to a manager, giving her this exact scenario, and she said they would hold it until close on the 24th. After that, see ya' later iPhone! We went back and forth with me "are you meaning to tell me, that if you are out of iPhones at noon, except for the one I've reserved, and there are 500 people in line that want a Phone, you will hold it for me until I can come in at 7pm after work?!" And she said "yes." She looked at the email part about first come first serve, and said that it's true AFTER your reservation lapses. She said having a reservation is better than showing up without one (i.e. spending the night).
In addition, she said to not even bother coming in at 7am (I would have one hour to get the phone before work), and to avoid the chaos. She took my name and gave me her word . . .
Makes me feel uneasy, but it's the only choice I have, considering my summer location is not my billing address. Else, I would have had it shipped.
Good luck to you all!