Iko,
Just boil until boiling point I think.
I dunno leh, I think so, cos my maid boil one big pot for the day. Then I drink cup by cup. Then reminder cold already, just add hot water in.
I think better boil it rather than put hot water cos got sugar mah. If u dun intend to put sugar then no need boil bah.
Yesterday, my first time doing it, never remove the skin, and cook it, taste so bitter... So today tried no skin, taste so much better.