OK so your mailbox was empty when the first wave went out and you want that Beta key. Blizzard posted a reponse the constant “Where’s my key Blizzard!” and “Are you sending more keys today” comments. The answer is what you’d expect, as has been stated a million times, they will go out in waves 🙂
The Blizzard folk who are monitoring the concurrency trend of people online and playing, as well as the stability of the game servers, will do waves of invites as needed. When I say “as needed,” I mean when the servers are stable and we’re comfortable with the room we have to get more people in the game. We won’t do waves of invites if we feel our infrastructure at any given time can’t handle an increased concurrency.
Beyond that, there’s really only an extra morsel of information — small though it may be — I can provide as to when invites might go out. They’ll go out, as I said before, when we’re comfortable with increasing concurrent players online. And they’ll typically go out during standard business hours (9 a.m. – 6 p.m. Monday – Friday, North American Pacific time).