They usually do send out a ding when it entends, but the did not send it yesterday. It opened up yesterday at 11:20 EST.
We are also a family of 6, and yes you check in right at the 24 hour mark to get your A passes and you can sit together. If you have any really young ones you can do the pre-boarding, but they board after the A's so it is better to get your A pass.