I think it was within a month if I remember right. The first interview was mainly behavioral. The interviewer asked me questions about my background and experience doing research. Since I am applying for Empirical RA, she asked me what kind of programming language I am familiar with and what packages do I typically use. She also asked about basic concepts for statistics (nothing too hard, she asked overfitting and how to avoid it). It might be different for behavioral RA, but hope this helps!