Wanna7.5,
IMHO, a lot depends on the type of microwave, how much rice you’ve got in the sock and how beat up your penis is from the last session. I read some guys here heat their sock up for 1.5 minutes. I have 8 oz. of rice in mine and at best, anything over a minute is extremely uncomfortable. And if my member is still sensitive from the last session of PE or wild sex with my honey :) even a minute can be too much! I’d recommend starting at 30 or 45 seconds and bumping it up 15 or so till you find the right temp.
Word of caution, I’ve noticed that the sock can get “hot spots” in it after microwaving and even if it doesn’t feel hot under my fingers, when it wrap it around my penis, I end up letting out a yelp. So I massage mine with my fingers to check the heat and move the rice around a little before applying it. Of course, your mileage may vary.