I can't find any direct reference to the cooking times in On Food and Cooking. Do you mean the bit on utensil materials right at the back?
Anyway, I would think silicon is a poor conductor of heat (as it is warm to the touch, and they make oven mitts and oven pans out of it but no stovetop pans) so basically the bit about ceramics and glass applies - except they are not susceptible to mechanical stresses.