First off, congrats for booking your first session of therapy.
This is just my opinion.
I think you should make your intent clear at your first session that you want to start hrt. A lot of people do that. I do that. However, I don't think you should look at therapy as, "just give me my letters". Take that time to explore yourself more as a person, since being trans isn't the only thing about us. Then, again, if you don't have that type of time or money, and you really want to focus on getting hrt, then the best thing you can do is tell your therapist your plans. Let your therapist know your plans and that will let them know that this is something you researched deeply. At my first therapy session, I let my therapist know what my plans were exactly and I think that helped lay the ground for further sessions.