I had some noticeable change after about 2 weeks, enough for others to notice. But I will note that it was still within my previous range, just on the low end, so that might have been placebo effect as well. After that I was gradually able to reach deeper notes than before, and my speaking voice started to change in more ways than depth - resonance, maybe. I retained my upper range for maybe 2 months, with some effort... then I stopped trying for a few days and it was gone.
I didn't feel anything at all different with my throat, except when trying to reach higher notes. Then I felt a tightness that increased the higher I tried to reach.