The design of my IHD is so bad.I turned down the brightness to its lowest
Basically when the screen is deemed active, the brightness setting actually doesnt do anything, its always full brightness.
Its idle mode will them dim the screen and it takes a while to do this as well, which is what the brightness setting adjusts. It actually never turns off the screen based on idle usage, it will stay on until the battery is dead or forever if plugged into mains.
Whoever designed these was a bit of a muppet in power management.