When is the right time to flush automatic gearbox?

[skyline2m]

I just want to ask when is the right time to flush my automatic gearbox
How many kilometer?
Is there any mark
currently my gearbox is not goin very smooth especially when the car is stop and then shift to reverse(R) or drive (D) gear, it got sound "ting" once

 

[JINEIL2EN]

20000km change the fluid, 40000km flush the gb.

 

[piazza]

or whenever you see the ATF is no longer in its pinky color and already changed to dark red, with residue when you wipe the ATF dip stick with white cloth or paper.

 

[amTonjet]

or whenever you see the ATF is no longer in its pinky color and already changed to dark red, with residue when you wipe the ATF dip stick with white cloth or paper.

~~~agree~~~