When I flew for GK, we used to have a 48-hour layover in LAX after a flight from LGW. This proved to be not good for your health for you were on the ground in LAX just about long enough to start getting into local time.
The result of this was that you were doubly knackered on return to UK with two lots of 10-hour time shifts.
We went on to 24-hour layovers after a while and, whilst it was not so much fun socially, it was much kinder to the body for you never really got into Californian time.