I tried to do the daytime crossing JFK-LHR twice. The first time, back in 2008 or so, was on New Year's Day. The CRJ-900 I was supposed to board at DCA at 0600 had been diverted to IAD the night before because of high winds in the national capital area and didn't show up at DCA until 0630. When we landed at JFK and rolled up to the old RJ corral (at current gates 64-66), I could see the connecting flight to LHR pushing back. A wonderful concierge in the T2 Crown Room came to my rescue and handed me a BP for a J seat on the 2000 departure (I had a cheap coach ticket). As things turned out, I spent the day eating at a fantastic buffet in the restaurant at nearby Aqueduct and betting the ponies.
A few years later, Mrs. ND76 and I successfully connected from a Delta Connection flight from DCA to the VS 0800 departure. We had breakfast in the Clubhouse, and then sat in the extra legroom Y seats. The flight landed on time sometime around 2030, but it took us at least 90 minutes to clear immigration as we arrived at the same time as an Emirates A380. We took the tube to our hotel near Paddington station and didn't get there until about 2300. I think we ate dinner at Garfunkel's, which stays open late. We decided that we would rather fly overnight rather than do that again