Last year my interviewer was an admission officer. I also heard that some students' interviewer were 2nd year students. And for Chinese students, if you are in China, normally it will be telephone interview. However, I heard that AD may arrange a face-to-face interview session in Shanghai on early Feburary.
About waiting time, I need to consult with admission office first. Will turn back to you, if I get the answer.
I have submitted the material before 15 Dec and am expecting the interview.
Now I am currently working in Singapore and will go back to Shanghai for Chinese New year. So I am not sure about the location of interview. Let me cross my fingers and wait patiently.