Hi Terry,
It took us 6 hours. We left our home at 6:40 AM and arrived at the Empire Farm Days parking lot at 12:40 PM. This included two, minor 'where are we' excursions /w3tcompact/icons/blush.gif, even though I had the StreetAtlas maps. Plus we ran into some delay coming through Watkins Glen because of the traffic created by the those attending the NASCAR race. I would estimate that 5.5 hours would be the normal travel time. Going to EFD, we went up the east side of the Susequehanna River, coming back we chose the west side by picking up Rt 15 in Corning, NY which was a much more straight forward route.
I just did a StreetAtlas run for you and the Quickest route is I81 to Harrisburg, PA, US15 to Corning, NY then Rt 414 to Seneca Falls. Total time 6:23 and 293 miles. Based upon our experience, this time and mileage is pretty accurate.
If I had to do it over again, we would have arrived the night before, but my wife had to work until 8:30 Wednesday night, so leaving Thursday morning was our only option. Most of the wineries we passed don't open until noon for lunch. We didn't have time to stop on the way up and they weren't open on the way back. The Corning Glassworks would have been another nice place to tour as well as some of the other sites near Watkins Glen, but we didn't leave enough time. Next time.