HBS published an update regarding round 2 interviews on their admissions blog:

“Interviews happen with a member of the Admissions Board who has read your application and comes prepared for a friendly and deep conversation about your background. We invite about 1 in 5 applicants to interview with us. Typically, just over half of those interviewed are admitted. On January 28 and 31, we will send out our Round 2 invitations to interview. We send them out in two batches to make for a smoother interview sign-up process. I’ll post a bit more about the logistics as we get closer to January 28. For now, sit tight and try to enjoy the next week or two!”