When it comes to coming out on the job, I always recommend holding off as long as possible. Because this is so expensive, and the last thing you want is to lose your work while you're in the midst of transition -- it's much, much harder to get a new job when you're so vulnerable.
Aside from that, so much depends on what your long-term plans are. If passing is important, and you plan on living a life without a "trans narrative," you might consider not transitioning on the job at all. Rather, after getting to the point where you're not getting clocked, and you've got all your documentation changed, just move on and get a new job (in a new city, even better) where no one knows.
I never came out at work -- thankfully, I was a telecommuter, so after I got all my surgeries taken care of, I left that job and started a new career. And I'm so happy I did, despite the difficulties of doing so.