Probably took 6 months or so - the process was drawn out because I have a lot of family as JWs ( including elderly parents ) and to go "cold turkey" & leave in a very short time period would have been difficult logistically.
I eventually came off as an elder & the plan was to stay and intermittently attend meetings for a few months and then fade completely but that step only took 6 weeks or so. I had always been involved in the meetings and invariably had an item ( or two ) every week and was the TMS overseer - I hadn't realised that the meetings are so boring and pointless when you aren't involved in any way and I just hated them & my kids didn't want to attend either. I went on a vacation abroad & decided while I was away to never go back.