This August, I helped my sister practice for her Columbia early decision interview. She is now CBS Class of 2021!!
I think she had a little less than a week of practice.
She practiced with a consultant for 1 hour, with me over the phone for 40 minutes, with two other friends. The night before the interview, she read a book published by a Columbia Business School professor. She's also been following the school's Instagram account for a full year and had great suggestions on their marketing techniques (her post-MBA goal is in marketing).