Sorry for the delay in responses, but I'm working today and I have been asking a friend who went through the process to give me details on logging into the pre-order website...
This is the message I recieve when I try to log on. What does that mean?
There are no valid service accounts.
A service account is a sub-account that is kept under your Square Enix ID. Any time you register a game it creates a service account, so you'd have one for FFXIV, FFXI if you played that and/or for each copy of the game you register if you have multiple copies of a game linked to the Square Enix ID. The website you should be using is this one.
Log in to that website, input the 18 digit code, select the platform that you wish to play on and submit the info. You should be directed to another page with a link to download the launcher(not necessary if you have the updated client from the last phase of beta) and you should also see a code displayed. This also means that the early access is active on your account.
Open the launcher and log in. The launcher will ask you for the code that was displayed on the website. Enter the info there and you should be good to go.
So apparently the Launcher recognizes my account but thinks it is a Eu account.
While the NA site apparently will only accept new accounts.
Log into the same website you linked above. Click the 'Log in' button at the top and fill in the username and password with your Square Enix ID information. You should see your name where it used to say log in now. Click your name and go to profile. Click the settings button. This should take you to a page to enter your info. Make sure you fill it out completely and select 'English(US)' as your language. Submit that info and go back to the main pre-order page and see if it works now.
As far as the dates, I'm not sure why it's like that. Perhaps they will only give the bonus in-game items up until that date? If I figure out why I'll post again, but as far as we know early access started today and runs up to and through launch which is Tuesday.