The HBS invites/decisions have always come out once a day for the days they have identified. Today's time was 12:00 -12:03 noon EST. Sandy has a number of clients from HBS so he usually does an estimate of % of invites sent based on his pool. People who were scheduling interviews last year were also able to give the forum an approximate count about how many interview slots were open per location. (that changes as they open more slots periodically, so its not an ideal indicator)
Congrats to Lala10 and to all the interview invite recipients! GMATClub has an interview practice setup on Skype described in a page linked on my signature - feel free to organize yourselves and do mock interviews with each-other to prepare for the interview.