I did it 5 months after HRT, 3 months after going full time.
I think it's definitely worth giving voice training a shot, and it's never too soon to start practicing even if you haven't started hormones yet. A lot of people do really well with voice training- there is no reason to completely write it off that you will never succeed with that alone!
For me I was becoming VERY happy with my voice in private, but stage fright always got ahold of me and I felt completely fake using it anywhere in front of friends or in public. Usually my feminine voice could last a few seconds, and then I would feel like a fraud and it always slowly sank back down. Thinking back to those times makes me shudder and smile all at the same time.
I know I could have tried harder to assimilate my female voice into everyday speaking in public, but I sensed a HUGE amount of anguish I'd have to go through to really break through- and I didn't want to deal with that. I randomly had the money and the perfect companion to accompany me on a very interesting journey to Korea (where I would have to be a mute).
It all happened in kind of a flash, but deep down in my gut I had absolutely no doubt it was the right decision for me- and I'm glad I did not falter with that life altering choice to book the surgery.
Now, halfway through the full recovery period, I can't imagine my life any other way. The inner confidence I have been able to grasp I would not trade for anything.
Moving forward, I hope that my high upper range continues to extend and become more accessible. So far, it is. I am still constantly learning new inflection techniques and ways to access those higher pitches. It's still largely a mental game in that regard- but because the voice sounds feminine no matter what, I find new vocal techniques to be much more easily integrated.