Remove the Delay for Auto-Hide & Auto-Show of Dock
Launch the Terminal and enter the following defaults write command:
defaults write com.apple.Dock autohide-delay -float 0 && killall Dock

Return to Default Dock Hide/Show Delay
To return to the default setting and autohide delay, go back to the Terminal and enter the following command:
defaults delete com.apple.Dock autohide-delay && killall Dock

http://osxdaily.com/2012/03/27/remove-auto-hide-dock-delay-mac-os-x/