Link: (Webkit) More Responsive Tapping on iOS
Webkit has disabled click delay on non-scalable web page in its nightly build 2 months ago. And here is an update with mention of the touch-action CSS property.
Putting touch-action: manipulation; on a clickable element makes WebKit consider touches that begin on the element only for the purposes of panning and pinching to zoom. This means WebKit does not consider double-tap gestures on the element, so single taps are dispatched immediately. Single taps on an element become fast when any of the element’s ancestors have the touch-action: manipulation. Note that putting touch-action: manipulation on any node opts all children of the node into the fast-tap optimization.