In brief
transition-delay sets a wait before a transition begins after a value changes. It differs from the duration of the movement itself.
Useful to know
transition-delay sets a wait before a transition begins after a value changes. It differs from the duration of the movement itself. [1]
For a menu, delay can affect perceived responsiveness. Check pointer entry and exit rather than only one activation. A long wait can make a working control appear unresponsive.
Sources
For further detail and to check the information: