I wouldn't have a problem with "stepping away from the helm" to stretch you legs, look over the side, or something like that (for about as long as you can hold your breath as I mentioned above). I would not go below to make a sandwich. Things happen faster than we realize. I would expect PWC's are pretty common on the Hudson, and they certainly can show up out of nowhere.
We had an autopilot and used it all the time, never left it alone though (we always had someone to switch off to). As I mentioned, one of the best things about it is that it allows you to concentrate on your surroundings more (traffic an floating stuff) and not have to worry about a zig zag wake (course).