To effectively treat your water with any water conditioner you need to know as much as possible about your water supplier. The City of Chicago, my supplier, increases chloramine, chlorine, and buffers due to certain weather conditions, more so in the winter. I double dose the replacement water only, at times triple, most tanks get filled with a hose, no matter if I'm doing a smaller 30% water change, or a larger 80%+ one. I'm another one that has been mixing hot & cold for years, never had a problem.
In the summer, especially during fair weather, the water runs through the system at a quicker rate, they go easy with the additives, and I can get by with plain sodium thiosulfate.
Seachem states that Prime can safely be used at up to 5x the normal dosing rate. This being the case a little extra won't hurt, and might be a good idea if you don't trust your supplier, or don't know much about how & why they do what they do.