mine lasted for about six months, starting with sessions every two weeks for the first half and moving to once a month for the latter half. I don't remember the timeframe precisely, I think I did a total of ten sessions. it was around the second or third month that I was comfortable enough with it that it became "normal" I guess to talk, not having to actively think as much to talk, and by the end I think my voice "passes." During this time I was pretty inconsistent with practice due to .
If I'm being frank I didn't end up at the place I wanted to be, but what I really want is like Badass Contra-Alto which is like basically the hardest possible end point to get to with a "feminized" voice xpp