I chose to wait the three months before ever mentioning HRT to my therapist. He had me complete an assessment on my feelings towards HRT related issues and if everything go according to (my) plan, I'm going to ask for his approval to start AAs after our next session. That was the plan we agreed to the last time, with full HRT in a couple months. Funny thing is, I don't think he would have made me wait the three months had I asked about HRT sooner.
As other people have said, forget timelines. The important thing is for you to understand the process of HRT as fully as you can, and demonstrate that you're prepared to handle the changes it will bring. I keep thinking of it like trying to defuse a bomb. If you know what you're doing, its relatively safe. If you're not prepared to handle it, it will blow up on you.