In the past two months, I did two late flights, i.e. 10 PM, IAD->LHR/FRA. I pretty much skipped the food (just had the UA ice cream sundae) and was able to get about 4-5 hours of sleep. Of course this was 'lie flat'. By the time I exited from LHR and got to my hotel in Kensington, I only had a short wait for my room. And I stayed out and about until about 10 PM. For the FRA flight, I had another long haul, so hard to judge. But I think I'll continue with the late flights and hopefully hotel status will assist with early check-in.