I always use a mug infuser for my teas, and when I infuse tea that requires something below the boiling point for the water, I start with boiling water in the mug and then wait for a fixed amount of time for the cooling to occur. I had been estimating this, but recently I did a rather careful measurement of it, pre-heating a good, accurate thermometer to the boiling point and then holding the bottom of it in the center of the mug to get good readings.
Starting with a thick-walled 12 oz. mug at room temperature, here's the data:
Immediately after pouring - 202 F (heat going into mug, etc.)
1 minute - 190 F 2 minutes - 179 F 3 minutes - 172 F 4 minutes - 167 F 5 minutes - 163 F 6 minutes - 160 FRandy