Sorry, but I no longer have the card. However, the card they are flashing looks like this:
On the back side, it has your date/time window that you can ride. As long as your card is valid, you can ride as many times as you want. The preview from 5/12-5/14 is for Magic Kingdom Operations only and is NOT extended to merchandise, custodial, photopass, entertainment, etc.
They may start randomly asking people as of this weekend, but it won't be a soft opening. I asked a Fantasyland leader at unload when I used my ticket and as per the leader I spoke to, it will be more of an invitational magical moment. I have no idea if what this leader said was true, as I never met him previously.
Edited to quote the image to allow easy removal, if needed.