Probably because it is so variable depending on soap formula, mold, ambient environmental conditions (air temperature, humidity, etc.) Your own experience with your own formula and your particular mold, etc. is more likely to give you predictable perameters, but you might have to do a bit of observation & testing to come up with what works in your situation to identify your 'minimum' time & heat.
Sorry I couldn't point you to a more definitive answer, but perhaps if you search the forum for specifics about your set up, maybe one of the threads you find might give you a clue or you could contact a still-active member who has a set up similar to yours to ask if they identified a minimum time & temperature for gel.
ETA: In 2015, Amy Warden did a
blogpost on using PVC mold for soapmaking. It won't answer your question, but the Q&A portion has some information about non-gelling based on thickness of PVC and ambient temperature and soap formula impact on heating and gel.