The interview process takes different minutes based on how prepared or unprepared you are. However, I would advise you check background info about the NGO and understand their purpose before the interview date.
I applied through a staffing agency. The process took 2 months. I interviewed at Windle Trust Kenya (Nairobi) in Mar 2014
Interview
I was invited for the interview It took two months for me to be hired. I was scheduled on a convinient time and it ended up nicely where I haf a good intention for the post. Months later I was given a call by the Human Resource Manager saying that I was the successfull candidate.