While reverse engineering the Dock for HyperDock, I stumbled over this useful hidden setting that removes the display delay when the Dock is hidden.
To remove the delay, open Terminal, type or copy and paste the following line and hit return:
defaults write com.apple.Dock autohide-delay -float 0 && killall DockTo restore the default behavior, enter:
defaults delete com.apple.Dock autohide-delay && killall Dock[kirkmc adds: This is a nice hint. It has always annoyed me that, when moving the mouse to the side of my screen (I keep the Dock on the left side), there is that half-second delay before it displays. I've applied this setting and will use this permanently. It's not that a half-second is a long time, but my brain expects the Dock to appear more quickly, and it is always stymied by the wait.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120326061614691