"...How long do the soap in the bags need to be simmer for it to gel?..." The real answer is "it takes as long as it takes". The recipe, your technique, etc. will all affect this. SaltedFig mentioned about 30 minutes to gel. I think mine are taking more like 45-60 minutes to reach full gel. See my pics and notes in post 43. I can see that time might shorten with more practice with this method, but that's what it's taking now. I'm keeping the temp of the water bath about 180 F (80 C). That's plenty hot enough to drive saponification. I would worry about using a full boiling water bath (212 F, 100 C). For one, the hotter the temp, the harder it is on the fats -- heat increases the rate of oxidation of fats and thus will increase the chance of rancidity. For another, temps at or near boiling can cause soap to expand in volume and water to turn into steam. This will cause pressure to build up in the bag. Most people want to avoid this in a "normal" soap making method and you definitely don't want this to happen when using this sous vide method.