Since windows in macOS cannot overlap the Dock, hiding the Dock often provides an effective way to gain additional screen space. This can be particularly helpful for smaller screens.
Unfortunately, a delay always occurs until the Dock reappears when moving the mouse close to it.
Fortunately, many hidden settings in macOS can be altered using a command line utility named defaults. To trigger the Dock's fade-in animation instantly, hence completely disabling the delay, you have to enter the following command into the terminal:
defaults write com.apple.dock autohide-delay -float 0
killall Dock
After executing this command, the Dock needs to be restarted (killall Dock).
To return to the default behavior, simply delete the set key.
defaults delete com.apple.dock autohide-delay
killall Dock
Alternatively, the duration of the delay can also be set individually, in the following example to half a second:
defaults write com.apple.dock autohide-time-modifier -float 0.5
killall Dock