how long to lower temps When living quarters at 100

2 A/C units for an RV of that size is going to provide minimal cooling. If a 3rd A/C unit is an option it will make a dramatic improvement if you plan to do a lot of hot weather camping. If that's not an option or you don't do that kind of heat too often then running the genset and A/C at least a few hours before arrival will help a lot. I would use the air dump option during travels and then return to ducted A/C when you are going to occupy the unit.