I didn't follow candiFLA when training my voice, but it was normal for me for my voice to feel tired and a little sore, especially in the beginning when I had to talk for hours in one go. In my experience, I think it is part of building up endurance, just like when you train yourself to run longer and longer distances. After I built up my endurance, my voice never feels tired or sore any more when speaking. (It still does though after singing.)
But if my voice actually started to hurt, I would always, always stop using my voice completely for at least 5 to 10 minutes. That's definitely dangerous. School teachers who talk until their voice hurts and ignore it often end up with no voice at all for months, and it might even need surgery to fix. Not good!!