I looked at the change in tide at the mouth -- then checked the mid-bay situation. With his boat, I would suspect DDW can motor close to 7 knots when he wants to in flat water without too much touble. (Not quite as fast as your speedster, but...)

The speed of current may change (because of the upstream rainfall flow and, sometimes from wind direction amplifications, and sometimes because of extreme tides); but the time of the change in direction is usually pretty close to the timing of tidal "curves".

I checked the tidal stations, on the Delaware, it's pretty well covered.