Omari's traveling this week, but I may be able to shed some light on the situation. Definitely don't read too much into the timing of the invites. In our case three years ago, we both applied in Round 1, and I think Omari had already interviewed before I even received my invitation to interview (we both were admitted). I'm not sure if it was LIFO or FIFO or strongest first, but we didn't notice much of a correlation between when people interviewed and whether or not they ultimately were admitted. HBS (and all schools) are very guarded about their process, but we suspect that it's at least partly random.
I believe the invitation to interview was sent by email. They pretty much named the date and told me where to go and when.
Also, don't take HBS' decision deadlines too literally. I received my invitation to interview by the Round 1 decision deadline, but didn't actually receive my letter of admissions until the second week of February, which was a week or two after the official Round 1 decision deadline.
Try to stay sane!
Good luck,
Scott
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Co-Author, Your MBA Game Plan