First of all, I took the psychotechnic test online. The results came by email in about 5 days, but they can take up to 7 days to come in. As a recommendation, you can ask for your results at their recruitment page, corresponding to which country you're applying, at Facebook. The time that it takes to get the results is independent of the results.
Afterwards, I had to take the reasoning test at their headquarters. The test isn't extremely difficult, but the time constraint is a problem. Their test sample online only shows how the questions will be in principle and teach you how to answer them, but in no way reflects the real difficulty of the test. A calculator is as important as a pencil to take the test. Wrong questions are not penalized, so answer as much as you can. The results took about 7 days to come in by email. If positive, they'll contact you later for your initial interview.
They called me from HR to schedule the initial interview. In the interview, all their questions were behavioral. They look for past behavior to predict future behavior, and will ask you about your past successes. They also look how you fare against their Success Drivers, and your integrity. In my case, the questions were made by a panel of 2 in a round table. They were extremely nice and polite. The interview was more of a conversation, I was asked about 12 general behavioral questions, but there were more questions regarding the answer that I gave to them. I strongly recommend answering with the CAR method. The interview lasted more than an hour, and I enjoyed it every moment of it. You can ask about the company at the end of the interview, but it is absolutely prohibited to talk about salary or benefits, or any kind of negotiation, as they said to me. They will grade you, and compare you to other applicants, but this always happens in each step of the process
If successful, between 1 - 2 weeks you'll receive an email notifying you if you go to the "Final Interview" (which is not always final, as told by my interviewers). I'm currently at this step; I cannot confirm or deny anything more. If I recieve an offer or not, I will edit this interview.
I hope my experience helps you in your application process.
My general recommendations:
* This process has to be taken seriously. It demands a thorough research of yourself and them. In my honest opinion, it takes a long time, but in the end, worth it.
* You are always compared to others in each step of the process. Prepare accordingly.
* P&G literally tell you what they want from you. Research about them and their working culture as much as you can.