It really varies. Some therapists (I've never been to one) may issue you a letter rapidly if they feel that you are ready, others may be sticklers for the SOC's "guidelines" (written while laughing).
If you're an American and you a) have no insurance or b) your insurance doesn't cover SRS (as most don't), there are ways around it (just as for a UKer). IMHO, it's really best to just go to Thailand. Many Thai doctors will operate if you've been on HRT and doing RLE for at least a year, and if you haven't got the letters that the SOC requires, they have their own therapists that you can have a session with once you get there. Whereas the SOC requires a lengthy process of therapy to be sure you're really trans, the Thai system seems to only care whether you're mentally competent and responsible to make your own decision. Of course, this is a bad thing if one isn't really transsexual, but if you know in your heart of hearts that you are, I think it's a good alternative. It all depends on how willing you are to take responsibility for your own decisions, and personally, I think that that is a superior view. Not to mention, and this is once again my own personal opinion, Thai surgeons produce better results for less money than the American surgeons.
Lia