Since SE's secure account management system does not show anything about FFXIV preorder registration, here's the easy-slash-only-current way to tell if you're good to go:

Launch the FFXIV launcher, and let it update if needed.

Log into the account you were able to get AND REDEEM a 20-digit code for. You should be prompted to accept a new license agreement slated to begin on 24 Aug 2013. Read, check box, click next.

You should then be back to the usual launcher start screen, and at the top-right above the "play" button it'll either say "checking" or something about having to wait for early release. Do nothing; let it sit for about 45 seconds.

If nothing continues to happen, your code took and you're good for early access.

If you are NOT good to go, anywhere from immediately to about 5 seconds or so the launcher will change to a screen describing that you're not registered for early access and will need to visit an URL for entering your 20-digit early access code (which is what you must use the 18-digit code at preorder.na.finalfantasyxiv.com to obtain, or wait for SE to send if you prepurchased from their store).

AFAIK this is the -only- way at present to know for sure that your PC-version early access is ready.