the temp will pass if its anywhere from 90-98F. they allow for a range but what you do not want is piss thats 100 as its hotter than your body....red flag.
read the directions, when i used it i put it in the microwave for 10sec, shook up the bottle and got a temp reading, idk if i needed to go another 5sec, then just get some spandex and tuck it up under your balls. good to go.
you can put the heater to help maintain the temp if you have to keep it tucked on for a few hours, i didnt but i only had like 20min btw heating and testing
good luck