Essentially if i remember how the original 1.0 Physical CE was, you got a serial number from the reseller that stated you had purchased the CE. When you registered that code with SE your account was credited with having CE and thus early access. You could download and play the game from that account for about 1 week or so after launch when most resellers would have had the physical edition out to customers. Mine ended up being delayed so I had to contact support for an extension of my code, but they were very helpful with that aspect.
I suspect that the servers will go down for maintenance for probably the week of the release and come up early for the early access people. If you have a key from the reseller entered on your account, you will be able to download and play the game without having the physical CE in your hand. Then when it shows up, enter the valid key it comes with and continue playing.