As soon as a user hovers over the ad once, it’s counted as a hover in your reporting.
We only register one hover per ad per page load. It’s not possible to mouseover several times at once or to register several hovers.
On mobile, hovers correspond to “touchstart” and “touchend” events in the browser which are usually triggered when a user is holding their finger on the screen in a spot over the ad (could be scrolling, reading the ad, etc)