Ippodo tea indicates that Gyokuro should be steeped for 90 seconds at 140 F (60 F). Suggested ration of tea to water is 2 Tbsp (yes, Tbsp!) to 3 ounces (80ml) of water. To cool water to the proper temperature, Ippodo suggests transferring the water three times by first pouring into a cup, transferring that to a second, then third cup, then the tea pot.
140 °F / 60 °C 1 min, 30 sec 10 g 3 OZ / 88 ML