Agreed - It'll be the back end servers validating your login that will govern when you can access the game. The disk will give you the client end, but until Frontier allow the authentication it'll be useless.
Developers sometimes spin up the back end servers early to cater for the various retail routes that the launch day restriction (it helps flatten any login spikes).
If you have bought disk rather than digital, you will also have to factor in the day1 patch. The disks will have been pressed some weeks ago so that they can be produced in the high numbers needed for retail. This means that last minute optimisation will not have been included on the disk and will need to be downloaded before the game can be played. (Developers in the past have back-end validated that only the correct version of the client connects, meaning that your disk version will need to be up-issued to 1.1 or similar before it'll work).
on the other hand - you could be lucky...