They probably stopped sending waves of invites because the people that didn't take off work to play the game most likely will not be able to log in until after they get home from work.
~5pm local time
I can't give any numbers for how many invites went out that aren't actually being used yet but it could potentially be a significant number.
Who knows.
I can't wait till I get in, until then I can come up with sneaky ways to knock my roommate out so I can play on his account.