If you have the Dock set to automatically hide and show, you will have probably noticed that there’s a small but perceptible delay between it being triggered and it actually appearing. This is by design, to make it more difficult to trigger by accident, but when you need to flick between items in the dock frequently, those wasted milliseconds can become quite annoying very quickly.
There aren’t any options to control the dock delay from within the System Preferences but it is very easy to adjust via the command line. The following commands will work on OS X 10.7 (Lion) or newer.
The setting to control the delay is called autohide-delay and its value is specified in seconds. Personally, I have this set to 0 so that it’s instantaneous but you can set it to whatever you like by changing 0 in the following command to your desired value. The default is probably around 0.3.
defaults write com.apple.Dock autohide-delay -float 0 killall Dock
To restore the default delay:-
defaults delete com.apple.Dock autohide-delay killall Dock
In addition to reducing the delay, you can speed things up further by specifying the duration of the Dock animation. This setting, called the autohide-time-modifier, is also specified in seconds. A value of 0 is instantaneous (no animation). I like a value of 0.4 which makes the dock feel very snappy whilst still looking pretty slick.
defaults write com.apple.Dock autohide-time-modifier -float 0.4 killall Dock
To restore the default duration:-
defaults delete com.apple.Dock autohide-time-modifier killall Dock
All settings take effect as soon as you kill the dock (it will automatically reload) so it’s easy to experiment with different values until you find what works for you.