The company took only a couple days to reach out to me and schedule a phone interview. After the phone interview, they wanted to interview me in person at their Chicago office about two weeks later. After the on-site interview, they extended an offer within days--all in all, the whole hiring process was very fast, only about 3-4 weeks.
Phone Interview: Very easy. It's with HR, and so it's very much an opportunity to simply introduce yourself, explain your background, and give them an idea if you're a potential employee. Don't expect anything technical, the HR just talks about the company.
On-site Interview: Laid back, conversational. A lot of attention is placed on your 20 minute self presentation. If you do a good job at explaining your coursework, your work experience, and your values, then there should be plenty to talk about. After your presentation, you get the chance to sit and talk with the individual teams (in my case, one interview with the Generation group and one with the Transmission/Distribution group). Don't be surprised when they ask you conversational questions like what your hobbies are, or whether or not you'll live in downtown. On the technical side, they don't expect anyone to be technically prepared for their kind of work since it's very non-theoretical, so don't expect any technical "quiz" questions.