Over 4 weeks, started with a phone interview with HR, followed by hiring manager, then onsite. The first two interviews were easy and quick: covered what I want from a position, how I describe myself, and resume.
The last interview was a full day onsite, with half an hour interviews back to back with all heads of the department, and one 1hr of a casual lunch interview with two process engineers I/II. I was given one break towards the end of the interview. In general, there were too many HR style questions (each interviewer came with 2 of these questions so that was a total of 20), and very few technical questions. In my opinion, the interview process was not representative of how a candidate will thrive in a process development/research/science environment: Didn't test prior knowledge/ability to reason through scientific problems/how one can work in a fast paced environment (which is what was asked of me in many of the other interviews I have with other companies).
They asked me to follow up a week later, which I did, and they told me they didn't have a decision yet. They said to follow up again a week later, which I did. Only then did they have the decency to tell me someone else had filled the spot.
They were professional - until the last interview step. I got two other offers from other companies within a week of the interview so I wasn't really bothered by not getting the job.