Hi Jim, we clean them in small sections at a time, no soap, and rinse, rinse, rinse, and rinse some more. We will use a 20% mix for direct application, or downstream if it's not really bad. When the weather is really hot outside we do them first thing in the morning, or we will even wait until the weather has cooled off. You just don't want your mix drying on the roof. Pre soaking the roof to cool it down like Richard says can also work, but the main thing is keep the roof wet. This is why we work small sections at a time versus applying to large areas like a shingle or tile roof.
I've never applied a wax to a roof. But I can;t stress enough to rinse, rinse, and rinse some more. Not using soap, or using very little soap, helps the rinsing go faster.