By default, mobile phones add a 300ms delay between tap (click) events and their action.
This is done to ensure the event is not a swipe (drag) event and they trigger the appropriate action.
But not for all cases this is recommended. Especially in buttons or links, which are not draggable elements at all.
For those elements Google FastButton is a script that forces mobile devices to trigger the tap/click action immediately.
Comes with a pure JS version, one for jQuery and one for XUI.