Interviews last a full day, and you get an agenda a few days in advance. I was given a week's notice before my interview. My interview was over webex. First I met with two panels of 3 researchers, each for about an hour. They asked about my interest in the Fed, my past research experience, some behavioral 'describe a time when' type questions, and a few questions about what I would do faced with certain research challenges. It's not a highly technical interview, but you should be able to describe your past major research projects in detail, specifically a senior thesis if you had one. After those first interviews, the rest of the day is mostly to help you learn what each section does so that you can rank your preferences at the end of the day. You will have panel interviews with different sections and hear about what they do. They may ask you follow up questions from the initial panel interview, but for the most part that time is for you to learn.