The interview consisted of various rounds. Sometimes the time between interview rounds took weeks, sometimes it had to be urgent and ad hoc. The case interview is interesting, and you have to prepare in advance, but they use the outcome of the case interviews to decide if and how they're going to pursue with that role. In other words, when they are doing interviews for a role, it is not a given that the role will actually be filled. Also bear in mind that for many roles, you will be hired as a freelancer.