It took about two years for me.
I had my doubts before, especially with changing doctrines concerning the "end times prophecies" And how they only seemed to change to suit the relentless passing of time, and how did that compute with guideance from the Holy Spirit. Yet, I've always somehow swept things under the rug, because whatever wrongs there might be, Jehovah would correct them in due time.
But only when I was seriously challenged by two different people regarding accusations of paedophilia problems with the JW Organization I began to investigate further into other scandals. That led me to Robert King's website/forum, then to JWN. I've come a long way, really.
Yet, even then, I only left when I successfully took my entire household family out as well.
Eden