I've always considered "arriving at my waypoint" to be when the transducer starts picking up an image of the cover I've marked.
But, for me, since the transducer to my GPS capable unit is on the trolling motor, I'm fishing well before that image appears on screen (since my rod tips are at least 12' in front of my transducer). Which, IMHO is good, because I want the baits to "arrive" before the boat/shadow is over top of the cover.

... cp