Of course, the great advantage of TATL travel is that there's much more to do compared to US Domestic flights - you'll get a meal, and drink runs, and - most importantly if it's a boredom thing - individual seatback IFE on all but a handful of aircraft these days.
UK to the East Coast is about 7 hours depending on exact destination - by the time you've eaten, watched two or three films and perhaps listened to a bit of music, you'll be within a couple of hours maximum of your destination. The US to Europe part is even shorter so the timings are even easier.
Of course, Business Class makes this all seem even shorter because the meals are much more involved so take longer and there's more drink runs etc. You're also much more inclined to sleep because the seat is far more conducive to doing so, which passes another hour or so if need be.
Certainly on evening departures from the US when in Business Class I now eat in the lounge, have an alcoholic drink on the plane to make sure I'm drowsy, and then get a solid few hours sleep.