How and when to put green tea leaves in hot water... It's more complicated than one can imagine.
First of all, there are 3 basic ways to add tea leaves in hot water in the case of green tea:
1, top throw (Shang Tou), add leaves after cup is filled up with hot water to top
2, middle throw (Zhong Tou), fill cup 1/5, then add leaves, let it soak for 20-30 seconds, then fill hot water all the way to top
3, bottom throw (Xia Tou), add leaves to empty cup, then fill with hot water to top
Which "throw" to use can be seasonal, summer and fall can use top throw, spring and winter can use bottom throw. Delicate leaves such as top grade spring Lung Jing or Bi Luo Chun can use top throw, medium size or hairy tips such as Mao Jian can be middle throw, Jasmine pearls should use bottom throw. The logic behind it is, the smaller and more delicate leave which can't take high heat should use top throw; while something needs more time to open up but can't be "cooked" with hot temperature use middle throw; something can with-stand or require higher temperature use bottom throw.