I managed to turn out an over 4,00 word short story using the voice recorder on my phone a few days ago. It took me about a day of thinking, and possibly 40 or so minutes real-time to record the story. It took me about an hour per thousand words to transcribe it.
I did some light editing as I was transcribing, and made another light pass when I was done. But I still have several hours of heavier work to really make the story gel. The bones are there, but the language and flow need some work.
I sound it difficult to "get into" what I was writing, while I was writing it. The story suffered somewhat for this, coming out far rougher than if I had typed it. Definite;y needed more editing, and self editing is more difficult for me when I am talking, and on the spot.
I don't feel like I really saved any time, versus just sitting down and typing. But I did use my time more efficiently. I can also see where, if I was more accustomed to the process, it might be more rewarding. It certainly is viable, enough so that I have started a second story using the same methods.
The next one I do, i think I am going to try treating it as somewhere between an actual draft and an outline, see if I can work up a rhythm. Like collaborating with myself. I do appreciate the time efficiency aspects of this method.
Also, it's really nice to come home from work, and go straight into transcribing, secure in the knowledge that I am going to make my word count goals, guaranteed.