After two phone interviews (a general one with the HR department lasting about an hour and a technical one with the hiring manager lasting about one and a half hours) I've been invited to the HQ for a face-to-face interview; the interview started with a brief talk during which both parties introduced themselves and proceeded with a second technical interview lasting about one hour. Afterwards I have been introduced to the rest of the team and had a half-an-hour chat before being shown around the building and being presented with the office facilities. Overall, I've been in the building for about two and a half hours.