I did some testing today. Remember the sun is very low. So, cook times will be much shorter other times of the year.

11:24------ 65.2 degrees out of the water filter tap. 8 ounces of water/ copper bottom pot.
11:29----- 144.1 degrees
11:34----- 172.2 degrees
11:39------183.9 degrees
11:44------ left lid partway off/ no data collected
11:49------192.7 degrees
12:00------203.4 degrees full boil