Is there an ideal time to apply? Is 100 degree weather too hot to apply this type of paint?
The ideal temp is around 75-80 degrees but it is possible to use most elastomeric coatings at higher temps.
1- Porous masonry surfaces can be pre-wetted by misting water to help extend the working time. Double check this with the manufacture. I have done this with a Sonneborn commercial elastomeric and Devflex. Don't saturate the surface, just mist prior to application.
2- At high temps rolling or brushing will be difficult. Don't over work the coating.
3- Work in the shade. Direct sun will only make the coating set faster.
Double check with the manufacture for additional recommendations.