The interview itself was a single day, where a large group of us sat down, and took a standardized test with a modicum of math, SQL, and programming related questions. Basic knowledge at best, and not entirely necessary from a long term perspective. More important would be the questions that the CEO asked. Aside from the written questions, based on conversations with current employees, the conversational questions asked by the CEO had a massively disproportionate weight; if you impress him, you get in. if you don't, a perfect score wouldn't net you a callback. Whether this is true or not, there's more than enough evidence on the employee side of things to credit it as true.