Here's the thing
There's your pace, and HRT's pace. If you are young, HRT is probably going to go faster than you are ready to. I stopped being able to pass as a guy long before I thought would be the case. I cannot *convince* people over the phone that I am a guy,which has actually lead to problems with my accounts. And last night for the first time, I had my driver's license rejected as a form of identification.
If you are young, and are starting from an easy point (high voice, small build), then within 6 months of full HRT you will probably be surprised. Of course, I was on AA for years before, so that may have made things easier for me - being on hair removal for years before certainly did.
The first thing you should do is start laser hair removal immediately, it takes FOREVER, is very expensive, and is incredibly necessary to pass.
I had to go the 3 months to get a therapist letter, it's part of standards of care. I did it via 2 visits - when I walked in her door, she thought I was full time already, and that was before estrogen. She wanted to see me more, but told me medical supervision and costs are more important for me. I really would like to see her, but I just can't afford to anymore. I was also on black market AA and E by the time she wrote it, anyway.
Good luck.