this question it might have many answers. It depends upon the circumstances of each indivitual. In my cases I lasted 5 years. I became innactive as soon I realize that my entire life was fake and based upon a lie, made by some humans who think they are "God's people". I was for 5 years innactive and then my ex-wife turned me to the elders for apostasy. She did this in fact not once, but two times!!! So I said I had enough of your religion and I gave them hard questions to the Judical Comitee(you know the ones you should never ask when you are JW)
As a result they refuse to answer and I said if you can't give me answers then I do not feel that I will going to support a religion that doesn't answers questions and request blind faith!!!
So actually it is upon you. The best thing it is to fade out so you can still associate your relatives and friends. They will just say that you are "weak in faith", and you don't have to go through the process of shunning