I'm stealth if I'm dating someone, until more comes up.
My last experience, it was a month and then I had to tell him (ur, we were in bed together -- he had no idea -- and it was a very awkward conversation, then we slept together, and now we don't talk to each other).
If I was post-op, part of me would not want to say anything until even further along. But then if I'm post-op, I don't know how much the trans history would be important. Since I'm pre-op, well, erm, it's hard to hide the parts once you're naked.
Right now I'm not really dating anyone. I'm not closing the door, but I'm not opening it right away, either.