Like others have already said: It's different for everyone and there really isn't a right or wrong answer.
Personally, I was over 20 months into HRT before making announcements and going full time. I'm 43, if that makes any difference at all. Honestly, my therapist was encouraging me more than anyone (myself included) to go full time sooner. Probably because she could see what living as a male was doing to me.
I probably waited a little too long in retrospect, I waited until depression was starting to take hold again and that was my final straw when I realized that. I kept telling myself to wait....... for HRT to do more, for my hair to be a **little**longer, for more electrolysis, to get more comfortable in my job, etc.....
In the end I just reached a point of "screw it, I can't handle it any more" and that was it.