Boiling water a little longer will increase relative humidity inside the room. Just like sweat has trouble evaporating while the air is saturated, the tea will also let off less steam after it’s made, and stay hot longer than it would if the air was totally dry. Don’t let the others fool you, when you already have discovered this yourself. It is hotter when you take the first sip when you boil it longer. It probably has cooled down a little bit from 100 degrees while on the stove, but not as much as it would if you took it off the stove right away.