Thanks to maximus610 and paco! That's what I recall as well, that the time limit starts when the candidate passes the last exam. I just wasn't sure about the time frame anymore (the 36 month).
At my flight school where I am currently doing my ATPL they informed the time limit started from your first exam sitting.
I'm going to take their word for it.
It's possible i'm wrong but that's what I was led to believe
That applies for to the time frame (18 month) in which the written exams must be completed (starts with the first sitting) as mentioned above (post#7) by maximus610.