The hiring process up to the interview took about 6 months. I had already accepted another job when GAO called for an interview. After debating merits, I took the interview and asked one of the interviewers via email for a reply ASAP due to my situation. HR got back to me the next day and I accepted their offer.
The interview itself was pretty easy. It consisted of a panel interview asking the basic behavioral questions. I would emphasis teamwork/collaboration, research and writing skills. Also mention any experience you have with interviewing people, editing papers and giving feedback.
The interviewers were friendly.